I love that if I sign up for a class, in committed to going. And I like coaches pushing me, where I otherwise may not do so myself. The only thing I've been having a problem with is getting charged for extra classes when I shouldn't be. Other than that, I've convinced several of my friends to join.
Intensity. Don't have to think about what to do because it's already planned. Coaches repeat instructions at each interval. Coaches explain and correct form when needed and explain how to prevent injury.