In my opinion, I don’t think they serve any purpose at all.
Having read the article in the reading section of the unit I would put myself near “dreams being meaningless waste products of the brain” side.
I don’t think they try to compensate for unfulfilled desires. I remember the next thing happening to me many times: just about seconds to go unconscious, I start thinking about something. Few moments later, this thoughts start to become an elaborate story. If something wakes me up at that moment I realize I had just started dreaming, but I wasn’t aware of that because it all had started with some normal thinking process.
I mean, for me dreaming it’s just the process of thinking but not actively controled. That’s why I said my beliefs are NEAR Evans, Crick and Mitchinson theories. Because I don’t think the brain “updates” anything or dumps useless information, either. I think it just continues a process that can’t be stop in any way. With no purpose.
What do you think?