I think every book I've written has benefited from my dreams. In Magic Under Glass, for instance, Annalie's curse came from a vivid dream I had some years earlier about a cursed prince. I say dreams are like playing the lottery because you certainly can't count on them to help you, but once in awhile you'll get an unexpected gift, and it can be extremely valuable.
When a helpful dream does come along, its effect can be almost miraculously potent. I've been working on Magic Under Stone and there is a character in it who is new to the book. He's actually (at least, as of this first draft) the secondary POV along with Nimira, so he's pretty important! He has an interesting situation and I WANT to know him, but I didn't feel like I really did.
The other night I had a dream where I was semi-in his shoes. The setting was all wrong...it was modern, kind of like those weird Fushigi Yuugi stories where the cast of hot boys from ancient China are all oh-so-conveniently reincarnated in modern-day Japan. But because I briefly WAS him, I got some insights into his personality and his background that I didn't previously have. When I woke up suddenly I knew him in a new way. I've been clamoring to write about him ever since this dream, whereas before it was just sort of "meh".
This isn't the first time such a thing has happened by any means...but the nature of these dreams never fails to amaze me. I've had any number of bizarre character dream experiences. Sometimes I get hit with a whole new story out of nowhere, other times, like with the dream just described, I am walking in a characters shoes and getting to understand them in a way I never could while awake. One time I even woke from a nightmare, calmed myself by thinking of my stories, went back to sleep, and had a continuation dream where my characters saved me from the threat.
Does everyone dream like this? Or is it because I sleep too much?