It is possible to use the stealth skill to "hide" in D&D 5e. But are there any mechanical benefits to doing so?
In combat, you gain advantage on an attack if your target can't see you, and confer disadvantage on their attack. Since you must be unseen to hide in the first place, what extra benefit does hiding get you?
Out of combat benefits might be harder to enumerate, but are there good examples where hiding might provide something more than just a good stealth check would?
Best to go back to the source on this; italics are my emphasis.
PHB p.177
Stealth. Make a Dexterity (Stealth) check when you attempt to conceal yourself from enemies, slink past guards, slip away without being noticed, or sneak up on someone without being seen or heard.
PHB p.177
Hiding
When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding, that check’s total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence.
You can’t hide from a creature that can see you, and if you make noise (such as shouting a warning or knocking over a vase), you give away your position. An invisible creature can’t be seen, so it can always try to hide. Signs of its passage might still be noticed, however, and it still has to stay quiet.
In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you. However, under certain circumstances, the Dungeon Master might allow you to stay hidden as you approach a creature that is distracted, allowing you to gain advantage on an attack before you are seen.
Passive Perception. When you hide, there’s a chance someone will notice you even if they aren't searching. To determine whether such a creature notices you, the DM compares your Dexterity (Stealth) check with that creature’s passive Wisdom (Perception) score, which equals 10 + the creature’s Wisdom modifier, as well as any other bonuses or penalties. If the creature has advantage, add 5. For disadvantage, subtract 5.
For example, if a 1st-level character (with a proficiency bonus of +2) has a Wisdom of 15 (a +2 modifier) and proficiency in Perception, he or she has a passive Wisdom (Perception) of 14.
What Can You See? One of the main factors in determining whether you can find a hidden creature or object is how well you can see in an area, which might be lightly or heavily obscured, as explained in chapter 8.
PHB Errata
The DM decides when circumstances are appropriate for hiding. Also, the question isn't whether a creature can see you when you are hiding. The question is whether it can see you clearly.
PHB p.179
Skulker
... You can try to hide when you are lightly obscured from the creature from which you are hiding. ...
PHB p.183
A given area might be lightly or heavily obscured. In a lightly obscured area, such as dim light, patchy fog, or moderate foliage, creatures have disadvantage on Wisdom (Perception) checks that rely on sight.
A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature in a heavily obscured area effectively suffers from the blinded condition (see appendix A).
Note: Darkvision in darkness is dim light and results in a lightly obscured area. Darkvision added to dim light gives bright light. Torches, lanterns etc give bright and dim light.
My takeaways from all of this:
Hidden means "unseen and unheard" (p. 195) so it incorporates and is superior to being merely "unseen". If the circumstances are right it can be better than invisibility without needing the spell.
Consider a combat with darkvision only (everywhere is lightly obscured). If there are things to hide behind (pillars, tables, walls) then the rogue can move behind one, hide and move anywhere that is no closer to the enemy with a good chance (Wisdom (Perception) at disadvantage) that no one knows where he is. Anyone targeting has to guess his location and even if they do they attack with disadvantage. If you are clever, you can move where the enemy is likely to move past you (AoO) on their turn or have your big strong Barbarian/Fighter/Ranger/Cleric companion grapple someone and bring them to you.
A party is camped at night in a featureless plain (i.e. no cover at all) and are attacked by a group of goblins. Now, goblins have this:
Nimble Escape. The goblin can take the Disengage or Hide action as a bonus action on each of its turns.
and
Stealth: +6
Assume that there is a campfire giving bright light for 15 feet and dim light for another 15 feet. Also, assume 2 (of 4) PCs have darkvision.
At the start of the combat, the goblins spread out around the camp and attempt to hide. They have time to get in position so let's give them advantage. As they approach they are "unseen and unheard" and have a Dexterity (Stealth) DC of [highest 1 of 2d20]+6.
A passive Wisdom (Perception) check is appropriate (with disadvantage unless the goblins are within dim light range and the PC has darkvision) to see if the PC on watch hears or sees anything as they approach to just inside the ring of (dim) light. A non-proficient PC with average wisdom has a passive Wisdom (Perception) of 10, -5 for disadvantage means he is not going to hear anything, ever. A 1-4 level Cleric will have a passive Wisdom (Perception) of 15 or 16, by 8-12 level this rises to 19 to 20 and at 17-20 to 22 say; the goblins will creep up un this gal about 80%, 55% and 36% of the time respectively.
If they are undetected, they attack with surprise, each shoots an arrow (with advantage if within the bright light) steps out of the light and darkvision range (5 feet). Attacking reveals their location, so they use the remainder of their movement (25 feet) to circle around in the dark to confuse the party.
Now the PCs are in a real bind - they have no targets (every goblin is in the dark) but the goblins can see them due to the fire. If they extinguish the fire the non-darkvision PCs are blind but the darvision PCs aren't much better off.
Every turn each goblin moves towards where the PCs last were, fires his bow (revealing their location) if he sees one, then moves out of darkvision range and hides again (without advantage). Now the PCs can move towards a given goblin, actively looking so we make active perception checks (with disadvantage for low light). What are the chances they find him? For Wisdom (Perception) modifiers of 0, +5 and +10 they are 12.7%, 30.9% and 55.5% respectively.
If they do find him, well the goblin was at least 65 feet away so without special abilities no one can close to melee this round; they can use a ranged weapon or spell or a saving throw type spell (normally overkill for 1 goblin but needs must).
If the goblin survives he can move, Hide (bonus action) and Dash (action) to start the cat and mouse game again. Meanwhile the other goblins are sniping all the while.
Be careful; this is a likely TPK for low to mid level PCs and even high level PCs will burn some serious resources.
Real world hiding
Just to remind you that people can be hidden without being invisible, can you see the sniper in this photo? Better be quick because they'll use their action this round to put a bullet in your head. You have 6 seconds if you use your action to Search.
If you didn't find them then you can practice with this Wired article.
So here's the thing: In combat, the Hide action is the only way to make enemies not know your position.
You can't attack someone who you don't have line of sight to, and if you have line of sight to them, they have it to you. If you duck out of sight and don't Hide, when you pop your head up to attack, everyone still knows exactly where you are, automatically counts as seeing you, and you don't get advantage on the attack.
In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you. However, under certain circumstances, the Dungeon Master might allow you to stay hidden as you approach a creature that is distracted, allowing you to gain advantage on an attack before you are seen.
Even when you do Hide, you probably aren't going to get close enough to a creature to melee attack them, which is why in 5e most Rogues use ranged weapons. (Which is bizarre coming from 3.5, of course.)
And here's the out of combat bit (note that this is just hiding, not the Hide action):
No matter how good your Stealth check is, it can't make you invisible. You need to at least make a token effort to hide (behind something, in the shadows, whatever), otherwise creatures will see you. It doesn't matter how silently you're moving if you're standing in the middle of an open field on a sunny day. Unless you say that you're hiding in the grass (or similar), everyone is going to notice you.
Three useful mechanical benefits:
It increases the chance that you'll be able to take advantage of surprise when you take the action to attack. However, that's situational. If you look in the rpg.stackexchange search bar for "surprise" you'll find a number of entries that discuss that mechanic. I'll not duplicate that here.
If you are in a party, the advantage to you is that someone else is likely to be the target of an attack.
Someone does not see you and passes you by thus providing you a chance to escape. Or, infiltrate. Tactically, the latter may allow you to get at their "second rank" or "rear" and get at the high value enemy unit: spell caster, leader, etc.
This discussion is missing the most important section regarding hiding:
"Unseen Attackers and Targets", PHB p.194
Combatants often try to escape their foes’ notice by hiding, casting the invisibility spell, or lurking in darkness.
When you attack a target that you can’t see, you have disadvantage on the attack roll. This is true whether you’re guessing the target’s location or you’re targeting a creature you can hear but not see. If the target isn’t in the location you targeted, you automatically miss, but the DM typically just says that the attack missed, not whether you guessed the target’s location correctly. When a creature can’t see you, you have advantage on attack rolls against it.
If you are hidden—both unseen and unheard—when you make an attack, you give away your location when the attack hits or misses.
If you know your enemies are going to use a certain path or come to a certain room, preemptively hiding at that spot is a great way to take them out without much risk. Indeed, if they do not know you are there (as in they failed their perception checks), they are surprised, which gives them tremendous penalties for the first round of combat.
"Surprise", PHB p.189
The DM determines who might be surprised. If neither side tries to be stealthy, they automatically notice each other. Otherwise, the DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn’t notice a threat is surprised at the start of the encounter.
If you’re surprised, you can’t move or take an action on your first turn of the combat, and you can’t take a reaction until that turn ends. A member of a group can be surprised even if the other members aren’t.
So, in essence, hiding allows you to gain one free round in which you can hurt your opponents while they can't defend themselves properly. If you plan well, that attack will most likely be executed with advantage (this might require a second stealth check, however, to leave your hiding place without being noticed).
Also, a Lightfoot Halfling has the ability to hide even when it's only cover is a medium or larger creature. This effectively means that a party with a halfling could surprise a group of opponents while in plain sight. If the rest of the party visibly poses no threat, the halfling could come out of hiding and engage combat, surprising the unwary foes and, DM permitting, granting the whole party the benefits of surprising their enemies.
If an ambush scenario is used, stealthy party members can take some time to assist their less stealthy partners using the "help" action (PHB, p.192), which can alleviate the penalties for wearing heavy armor or for having lower dexterity scores. Also, unless the targets are weary of an ambush and are actively searching for the party members, their passive perception sets the difficulty of the stealth check. This means that, unless ambushing people with high wisdom, the DC of the check should be easily achievable for pretty much everyone in the party, except perhaps for the str-based heavy armor user, who won't have advantage on the roll.
Yes, there is a benefit - you get to hide. :-)
Stalking a monster, sneaking through an enemy camp, getting into and out of the mayor's wife's room, robbing a store, eavesdropping on the evil high priest's plans, etc.
Remember that combat is only one of the three pillars of this game.
As to your last sentence - hiding is a stealth check. When a character is attempting to hide their presence from a foe, the game calls for a contested roll of DEX (Stealth) vs WIS (Perception).
