I almost thought of talking about Descartes' demon during this, because the ergo cogitat sum is a pretty big and important step in the philosophical development of knowledge.

For me, what I find is that dreams are a great way of tapping into things that you wouldn't ever say, but which reflect your position. There are people, including Carl Jung, who I highly respect, who argue that it might even go a step beyond that, and I don't necessarily intend to contradict them, but I don't see any evidence to support that.

One of the things that I found interesting recently was an interview with the author of a book called The Flat Mind, in which there was a lengthy discussion of the unconscious (e.g. the work of depth psychologists like Jung and Freud), which the author vehemently denied could exist but also pointed out that there was a deep mire of forces and instincts that impact our conscious perceptions, which is basically what the whole notion of the unconscious and subconscious is.

I think that our brains are great at forming narratives (I see this trend coming together in my readings in various fields, from psychology and philosophy to economics and history), and the dream is a great way to get a glimpse at our brain trying to form narratives. What exactly it has at its disposal when it tries to do that is beyond me, but I will say that after I manage to interpret a dream (which is not terribly frequent, and most of my dreams have no perceptible meaning) I usually figure out a solution to a problem in my life. I wouldn't be surprised if it's something to do with the memory formation process and a sort of re-analysis of existing information, which we perceive consciously through a half-active system and therefore witness as a passenger rather than an agent.