why we sleep?

Salam..you know why we sleep? let's check up..There are a few theories as to why we need so much sleep. One idea is that sleep is restorative to the body, giving it an opportunity to rest. But if rest is the goal, why does our brain remain hard at work? It's possible that while we sleep, the brain is practicing and running problem-solving drills before completing actions in the real world. There are several studies that show that learning can't take place without sleep to reinforce the knowledge [source: Schaffer].

Some of these studies may have real implications for students. One researcher claims that it would be better for students to review information until they were tired, then slept, as opposed to pulling an all-nighter [source: BBC]. Some schools have changed the time of that first bell so that middle and high school students can get a little more snooze time [source: Boyce, Brink]

thank you..