Thomas Edison claimed it was waste of time.

We spend a third of our lives doing it. Napoleon, Florence Nightingale and Margaret Thatcher got by on four hours a night. Thomas Edison claimed it was waste of time. If one can get by without the desire to sleep, one could watch latenight movies everyday like mad; stargaze all the time; always churn out last minute presentation overnight AND stay awake during the presentation itself etc. The amount of energy saved by sleeping for eight hours is miniscule – about 50 kCal, equivalent to a piece of toast. Now it does sound like a waste to fall asleep. So why do we sleep?

No one really knows why. What we do know is the effect of the lack of sleep. For all those who have pulled an all-nighter before, you would have noticed these common aftereffects of sleep deprivation: grumpiness, grogginess, irritability and forgetfulness. Concentration will be impaired and attention span shortened. According to studies, after staying up for about 18 hours, most people will start to experience bouts of microsleep — moments when you zone out momentarily. Reaction time slows down to that equivalent to a blood alcohol level of 0.05% (two glasses of wine). This is the legal drink driving limit in the UK. Your eyelids start to droop more severely, and by the 20-hour mark you begin to nod off. In short, sustained lack of sleep has serious impact on the emotional and physical health. 

Researchers have yet to find any vital biological function that sleep restores. As far as anyone can tell, muscles don’t need sleep, just regular periods of relaxation. Sleep or no sleep, the rest of the body chugs along as usual. It then seems to me that the function of sleep, if does not directly concern the physical body, could have something to do with the mind. Now I’m really excited about this project. 

:

http://www.time.com/time/magazine/article/0,9171,1006591,00.html

http://www.bbc.co.uk/science/humanbody/sleep/articles/whatissleep.shtml