Your interpretation of the rules is mostly correct. It gives +2 to hit but not to damage:
A character who spends a full round aiming (no movement
allowed) may add +2 to his Shooting or Throwing roll in the
following round versus whatever he aimed at (a person,
vehicle, etc.). Aiming for multiple rounds has no extra effect.
p.70 Savage Worlds Deluxe or p.79 Deluxe Explorer Edition, Situational Combat rules
Aim is a situational thing that when used is powerful. How much utility it gets depends on the types of scenario the GM throws at the players and how realistically NPCs react to situations. It also gets more use with clever teamwork.
If every map the GM uses has a lot of cover that NPCs can completely hide behind, aim will be less useful. With maps where there is less of this type of cover, avoiding enemies who aim at you becomes a lot more difficult.
Another factor is how NPCs are being played. If a GM assumes every NPC is automatically aware of a PC who is aiming and reacts accordingly, it will massively reduce its usefulness. When I GM, I try to play the NPCs more realistically. In the chaos of a typical combat it is not realistic to assume all NPCs will be aware every time someone aims. I might throw in a Notice roll if appropriate, or if an enemy is engaged with another combatant, they might not notice at all.
The type of enemy also matters. Combat-trained soldiers are going to react tactically to an aiming opponent, but a pack of wolves or other enemies who act on instinct would not.
Teamwork can also help. Aim gets a lot of use in the initial round of combat before the enemy is fully aware of the PCs presence. This is particularly the case if PCs are in a position they've allowed to prepare a little for. In prepared situations like this, I assume that PCs who want to can have been aiming coming into the first round of combat if enemies have been visible. If they choose to do this, I will generally give the opposition a Notice roll to spot them if they've made an attempt to conceal their position.
Teamwork also helps when you have melee characters who can tie up a target and make it difficult for them to retreat behind cover. As stated above, I often rule that an NPC engaged in hand-to-hand combat wouldn't necessarily see an aiming enemy if it makes sense. Also, if you give an enemy the choice between taking a melee attack from withdrawing from combat, or a shot from an aiming opponent, things become a lot more interesting. You can also attempt to reduce the maneuverability of enemies, e.g. by knocking them prone to reduce their pace.
So in summary, aiming is a powerful tool that is situational, and for good reason. +2 to Shooting rolls is a big bonus in Savage Worlds, and if it was always in play, then it would be too powerful. The GM can help by varying the circumstances and types of battlefields combat takes place on, as well as portraying NPCs realistically. Players can help by tying up combatants and making it more difficult for them to retreat behind cover.