Let's go back in time for a moment - way, way, back in time. We'll keep rewinding the clock until we reach the ancient times, and you can pick where we go: Greece, Egypt, Rome - whatever you prefer. Your decision is of little significance in this situation, since I'm mainly concerned with the concept of dreams. And, the idea of dreaming in the ancient world is almost entirely different than the one we have today.
During ancient times, dreams were thought to be messages from the gods, and there was a supernatural component linked to the meaning of dreams. Back then, dreams were an entrance into a spiritual realm - an exit from the physical world. They weren't necessarily associated with reality as we understand them today.
“The naive judgment of a person on awakening assumes that the dream… at any rate has taken the dreamer into another world.” - Freud
There is, however, still debate as to whether or not dreams are connected to reality. Thinkers such as Burdach, and Strumpell would argue that they aren't connected to reality, while Haffner, Maury and Hildebrant would argue they are.
“We may justly say that no matter what the dream offers, it finds its material in reality and in the psychic life arrayed around this reality. However strange the dream may seem, it can never detach itself from reality, and its most sublime as well as its most farcical structures must always borrow their elementary material either from what we have seen with our eyes in the outer world, or from what has previously found a place somewhere in our waking thoughts; in other words, it must be taken from what we had already experienced either objectively or subjectively.” - Hildebrant
If dreams are a product of reality, then the incentive to understand them increases. Often when I introduce the concept of dream interpretation to someone, there's a turnoff. My theory is that many in our society have yet to move on from ancient concepts of the meaning of dreams. If we can move past the idea that all dream interpretation is about predicting the future, communication from gods, or similar concepts, we might uncover some truths about ourselves and about reality.