From what I understand there is not a clear reason on why the brain needs to sleep - if I'm mistaken in this please let me know.
What science has discovered through observation is that if you don't sleep you seriously start sucking at everything. There are a few cases of people who
never sleep or almost never sleep, but they are exceptions - the rest of us needs to get our Z's in regularly to operate.
At least you know you're not the only one that gets messed up in this way - and the only way you could conteract this (without amazing willpower) is substance abuse. Stories of lawyers and wall street types snorting lines to work longer hours come to mind. But as the military and pharmaceuticals are working on
pills to keep you from falling asleep - who knows what to expect?