Just wandering the effectiveness of this spell. Does anyone really use it and where/how would you use it?

I believe the vanilla spell's effectiveness is based on your conjuration skill, so only casting it at a higher level will let you control the upper level daedra. It's useful when enemy mages summon atronachs if you don't feel like blasting them to pieces.

I have used the Spell against Dragon Priests and Draugr to turn Frost Atronachs.

Dragon Priests have used it against My characters.