Some desktop environments don’t provide a way to change the mouse acceleration (GNOME and Unity for instance), and even for those that do (like Cinnamon), you can’t completely turn it off. Here’s how to completely disable mouse acceleration in Linux (for Xorg). Disabling mouse acceleration is useful for FPS gaming.
Mouse acceleration makes the pointer movement depend on the speed with which you move the mouse, accelerating as you move it faster. So moving the mouse across the same distance can have different results, based on movement speed. In FPS games, this can make aiming difficult. With mouse acceleration disabled, the movement of the pointer is the same as the movement of the mouse, and it doesn’t change based on the movement speed. As a result, your aim should be more accurate in first-person shooters.