Without flaperons, guys would still be just flying 2D instead of 3D. On the right plane they will flatten out your spins, tighten up the loops.......the plane needs to have a light wing loading for flaperons / spoilerons to enhance aerobatics without the stall tendencies.
The average lead sled type of plane might make good use of them for achieving slower flight like others have suggested.....just go easy on deflection.