I heard that when we sleep that is when our 'soul' goes back to replenish itself from the one 'source of all things'. I guess another way to put it would be to say that when you're sleeping you're actually off to visit 'God' that's why you're not conscious or 'alive' during that time.
I think that the body doesn't really need to be asleep in order to rest or repair itself. I believe that the purpose of sleep is to replenish our mental energies. Of course I could be wrong, but I've found that in my life, the more in tune with myself I am (happy, passionate about something, eager to get on with my day every morning, and so on) the less sleep I need. Some nights I only go for 3 hours and yet the next day I'm as fresh as a daisy, ready to go again!
It's amazing that almost everyone has their own viewpoint when it comes to why sleep is necessary for us, but I think that the answer lies in all the different views expressed here.
I think it all depends on what you believe, which means that if you believe that you need 8 hours of sleep a day, but try to get by on 3, then you will undoubtedly have a problem. But if you are sure that you only need a couple of hours of sleep each night, then that is enough for you!
I think sleep is needed to keep the organism functioning efficiently and alive. Sleep-deprived people have disruptions in their biological processes. Lack of sleep is worse than stress for creating such disruptions.