I've only ever encountered it once. The BLM from my FC AoE-sleep'd a pack of mobs to prevent an over-pull with an undergeared, struggling healer, because I'd derped and messed up mob positioning in a dungeon.
In general, CC isn't that helpful. Stunning mobs works as a decent interrupt, but it's almost never a "STUN OR DIE" situation (outside of one of the attacks in A7).