I found it. You can read the entire article yourself here: http://msnbc.msn.com/id/3076707/

or, just read what I found interesting in it:

Think of the body as a car. No car can keep going and going and going without a tune-up or oil change. Human beings can function without a full tune-up, but they will be in a state of relative sleep deprivation and won’t be able to work or to think as well as they do when they are fully rested. It’s like an engine that gets only four out of eight spark plugs replaced and then runs sluggishly.

Lack of sleep clearly affects our thinking, or cognitive, processes. A sleep-deprived brain is truly running on four rather than eight cylinders. If we’re trying to be creative, the motor doesn’t work as well. We can perform calculations, but not as quickly. We’re much more likely to make errors. It’s because the brain’s engine hasn’t been replenished.

So, that's why you need sleep. If not for that reason, at least do it to avoid almost getting into two accidents on your way home from work and you only got around the corner. REMEMBER, SLEEP IS YOUR FRIEND!