1. Sleep is for restoration, to replenish and repair metabolic processes. Indeed, a whole host of genes are “turned on” only during sleep — genes associated with restoration and metabolic pathways.
(See Lisa Geneva’s Alzheimer’s talk, spinal fluid is released in deep / delta wave sleep to wash excess Amyloid Beta)
2. Sleep is for energy conservation, to save calories. This may seem an intuitive answer, says Foster, except that the difference between sleeping and quietly resting is about 110 calories a night, the equivalent of a hot dog bun. Not a very good upshot for such a complex process.
3. Finally, sleep is for brain processing and memory consolidation. This is the explanation Foster espouses. Studies show that if you prevent people from sleeping after a learning task, their ability to learn is basically smashed. And worse, our abilities to come up with novel solutions after a complex task are reduced after sleep deprivation.
Nice....number 3 confirms my theory as well....I also hypothesize that dreams are a visual byproduct of the processing and memory consolidation mentioned above. Think of a consolidation process that takes discrete memory fragments and seeks to organize them for long term storage. A dream is a window into this consolidation process.
https://www.ted.com/talks/russell_foster_why_do_we_sleep Russell Foster: Why do we sleep?