Of course, there are many theories as to why we dream. Science is hard pressed to actually explain the rapid eye movements associated with them, though. First I believed it was simply a by-product, a reflexive action that our brains would eventually learn to correct, if only for the sake of efficiency and not wasting energy.
I was giving this some thought last night, though, and I remembered readnig in some Psych texts that you can tell if someone is lying if they look at their upper right visual field before answering, since that (in theory) meant they were accessing their right brain (the creative) to make up a lie.
In this light, I suppose the flitting eye movements are probably not due to to looking or processing information faster than waking but to accessing different parts of the brain as fast as waking while letting the eyes follow their default action since they are not being used for sight.