You can sleep above level 50, and probably like below level 50 you can't just sleep anyone. Still usable as a stun alternative at level 80. In the latest dungeon where there's a couple charge AOEs it works, with enough of a cast time in their attack that you can fit a whole repose cast in, or if the timing is wrong from the previous cast swiftcast is possible. I only go with the trust system so otherwise there is no interruption. It's also good in fates where you pick up items. Really good in Eureka, especially black mage sleep because it's an AOE, also because black mage has two abilities that give instant cast. I did do a lot of solo black mage there for fun (before echo), but sleep I especially used for saving others/myself on the way to/back from NMs from high level targets that engage while going there, that would otherwise probably, if not in one hit, defeat them/me.