ESP hacks basically display data for you that in an unhacked Battlefield 4 game would not be visible to you. These can be things like player names, player health, player class, player positions, distance and so on. The most common one is the enemy player position on the map. So that basically means that you know where the enemy is no matter if you have UAV support or not and that is certainly a huge advantage to have in BF4. ESP hacks do work because even though the game does not display information like the position of all enemies to you, their position is still being stored in your game memory (RAM) and can be extracted and shown to you in various forms. There are also 2D ESP hacks that will either display all the enemy players on your game map or on a custom map, allowing you to track enemies outside your field of vision