its how sensitive the joystick is.

if you use an xbox controller you'll most likely be aware of the notorious design fault that is sticks to right or left in its default position, this tiny little direction can make your character run off wildy. Adjusting this setting higher (i think higher) will make it so you have to push the analog stick further out before your character turns in the direction and its not so sensitive.

similar for the back bumpers but not as important.