Differential ailerons are used to prevent stall due to aileron drag.
Stall due to aileron drag is more likely to occur on landing approach with flat bottom wings.
When the pilot applies aileron to roll upright during low speed, the downward movement of the aileron on the lower wing might take an angle on that part of the wing past the critical stall angle.
Since differential ailerons will have the opposite effect when flying inverted (but you're not supposed to land inverted), most aircraft with symmetrical airfoils designed for aerobatics don't use this system.