If I could answer that question I’d be sat here polishing my Nobel Prize! The bizarre thing about sleep is that it’s a biological necessity. We have to do it. Basically anything with a brain does it to a greater or lesser degree.
"Your brain is dealing with the day. It’s remembering the important things you need – and actively forgetting those you don’t."
We know roughly what sleep, or some of what sleep, does. Sleep gives rest to the body. Although that’s not really a strong need because of course we can get that during the day – I’m sitting here in front of my computer. I’m not using my muscles as much as I would do, my heart rate is down, my blood pressure is down because I’m sitting. Your body is repairing and recuperating all the time.
The most important thing about sleep is what happens during the deep sleep – slow-wave sleep. And that’s memory, learning and growth. You only grow during the night – during that deep sleep. That’s why children sleep so much. You’re also laying down memories. Your brain is dealing with the day. It’s remembering those important things that you need to remember and it’s actively forgetting the things that you don’t need. Your brain is sorting out all this information.
https://www.youtube.com/embed/stXhGMVJuqA?wmode=opaque
The other thing is you learn during the night. So it’s advisable to practice a task until you’re as good at that task as you can be before you go to sleep. After a good night’s sleep, you can be up to 17% better at that task, merely because you have slept. So, sleep is for the brain. It’s only during sleep that the brain’s activities reduce to any degree – during the day it’s doing so much.