I think there are two major problems with "hacking" one's sleeping patterns like this. First is physiological side effects that can go undetected for a very long time and cause permanent damage. Lack of sleep increases blood pressure, for instance.

Or the effectiveness of the thinking process itself (which is more difficult to measure) -- I was told at school that when I sleep my brain "processes and sorts information". Well if you reduce the amount of sleep four times perhaps you become more prone to make mistakes when working (and lose time fixing them).