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!