Crowd control is useless at higher levels because the mobs just simply resist every single crowd control thing. Silence, stun, and pacification are probably the only thing you can do in terms of stopping the enemy at higher levels. Sleep is pretty useful in case of screw-ups at lower level dungeons though. Sleep also works on SOME mobs all the way up to floor 189 at least in palace of the dead. It might have worked on one or two mobs after that, but i don't remember.