I've always wanted to try this, especially since I have bad dreams about exams the night before anyways.
Considering how random the stuff that shows up in my dreams can be, I'm not sure if I'd trust any of the information. I mean theoretically you could read your textbook once, then reread it in your dreams. But I think if you did that you'd be more likely to just end up writing "The purple polka dotted elephants can't swim." for your essays. Of course some people may have the control and attention to pull it off.

I think you could probably rehearse things easily, though. Like a presentation or something like that.

Lucid dreaming could actually be used to study things like organic chemistry and molecular structures. If you could just imagine the molecules floating in midair, it would definitely beat trying to draw them or use model kits! I was thinking about that the other day