Why do we dream???

To work things out

idk but a theory says that it's a way to get rid of memories. Like after dreaming we're supposed to forget some things. Which is why post traumatic people or people under stress dream a lot, though the mechanism goes hay wire and actually backfires.

Something to do with our subconscious/mind debriefing the days activities I read once.

Because reality is boring and repetitive.