Scale Mail, Chain Mail, and Plate all specifically mention that they include gauntlets. In the case of Scale and Chain, it merits a separate sentence:
The suit includes gauntlets.
Is there a significance to this that I'm missing? It seems odd that they would go to the trouble of defining which armour types include gauntlets and which don't if it's purely descriptive.
Do gauntlets do anything, or are they purely fluff?
That depends heavily on what you count as "fluff".
There is no defined mechanical benefit for wearing gauntlets. However, that doesn't mean that wearing gauntlets is not a thing that can be important sometimes.
For example, I was playing in a game recently where there was a sticky goop covering a floor. I touched it, but that made the goop rise from the floor and try to touch me. I took off my gauntlet, and the goop 'ate' it, without harming me. If I didn't have a gauntlet, then I would have been in trouble.
This is a big part of 5e in general. It's part of the design of the system that it's a lot more simulationist than 4e, and random things like having gauntlets, or a helmet, or other accouterments are intended to give you benefits that aren't explicitly spelled out in the mechanics, but still make sense in the fiction.
Think of it this way: How would you actually make use of gauntlets or other thick gloves in real life? That's the kind of benefit you get from gauntlets in-game.
While they have no rules regarding gauntlets yet. This could be an important piece of information such as when people are sticking hands where they don't belong; for example a drawer that's currently armed with a poison needle trap.
It also indirectly implies that lighter armors do not have gauntlets/gloves and there may be an impact with that. Thief types may wish to invest in a pair of gloves for safety.
It's basically fluff that can be used to enhance the game or a scenario at this point.
Speculation: There may be rules coming that govern mixing and matching armor pieces, and with magical items such as gloves and gauntlets this may have an impact. With only a few rulebooks to work with there is much that still may be put in place.
Mechanically, gauntlets do the same thing as other parts of the armor set listed in the item description - they protect the wearer, as a set. Like the helmet of plate armor, gauntlets are called out particularly, because wearing them might preclude wearing other items.
Fifth edition does not use a concept of item “slots” that fit on parts of the body. Instead, the item description details how a given type of armor is worn. Not surprisingly, armor that offers more protection requires wearing armor over more of the body. This can preclude wearing other useful items.
When a suit of armor specifies it includes gauntlets, you are not exactly wearing that type of armor when you are not wearing gauntlets. Since, “a character can’t normally wear more than one pair…of gloves or gauntlets,” (DMG p. 141) that means that if you are wearing magic gloves instead of gauntlets, you are not wearing your full set of armor. What this means mechanically is not spelled out, and would be left to DM discretion. (A -1 AC penalty would be plenty).
For mundane armor, the gauntlets included with the could be swapped out for another pair, such as Gauntlets of Ogre Power.
On the other hand, for magic armor that is a type that includes gauntlets, the gauntlets are part of the magic item. For example, plate armor comes in several pieces; no one piece is the magic item. What composes the armor “item” is defined in item description (in the PH, p. 144-145).
You can’t turn Platemail of Etherealness into Breastplate of Etherealness by only donning some of the armor. Likewise, you can’t swap out the gauntlets (or helmet) from the set, and still get the etherealness. Just as you need to wear both magic boots or gloves in a pair (see Paired Items, PH p. 141) you need to wear all pieces of the magic armor, including the gauntlets, to gain its benefits.
Well, there are specific Magical Gauntlets (e.g. Gauntlets of Oger Power). So, that's a consideration....
I think it's not necessarily 'fluff', because, hand protection is an armor slot (if you think of it like that), so, it's saying the heavier armors include that protection intrinsically and you don't need to buy additional gear to armor your hands.
Lighter armors require you to buy gloves/gauntlets to gain hand protection.
Also, it might play into earlier rules about mixing armor types. Plus, as Lord_Gareth stated, there were rules about unarmed vs armed combat.
I'd say they have as much use as either the player or the dungeon master give them. As a dungeon master if there's a situation that might cause players to drop their weapons I'd give anyone wearing gauntlets + to things like dragon breath or even only have players without them roll if they get a splash of acid on their front.
As a player if I knew my armour included a Gauntlet, I'd consider options putting a fist into wargs mouth if it got the jump on me (wouldn't do that without a gauntlet) or for taking off and throwing down at an opponents feet to challenge them.
Maybe things were different back in the 90s, but as I remember it, we rarely reached for the rule book on this kind of thing. If the dungeon master told me a Wargs bite strength was more than enough to shear through lobstered steel, then I'd just have to go running to the priest or learn to play a one handed character.
Reading another question, it brought up the whole issue of Encumbrance and Armor Penalties...such that, ok, heavier armors include gauntlets, so, encumbrance-wise, that weight is factored into the total weight of the armor versus piecemeal for other armors.
Also, a minor factor might be armor penalties to things like Dexterity -- i.e. you aren't going to picking a lock very effectively in plate gauntlets...
