It's hard to summarize. There is a lot of data and a lot of stuff to cover. I'll grab a couple of parts for you and I hope others can summarize others for you. :)

Why we need sleep:

Your brain needs sleep because your brain uses it to organized and optimized the experiences of the day. Without sleep your brain is unable to support new learning.

Read it, it's worth it. And if you don't think sleep is important enough to read this much about just start reading it and the author will convince you.