Is sleep the biggest mistake nature has made?

From the NYTimes:

Scientists are not sure why sleep exists at all, it is hard to explain the great diversity of sleeping habits in different species. For example, why should lions get 15 hours a night and giraffes just 5?

“We spend a third of our life sleeping, and it seems so maladaptive - ‘the biggest mistake nature has made.' But another way of looking at it is: unnecessary wakefulness is a bigger mistake.”

My opinion: I do not think sleep can be qualified as a "mistake". In any case, if nature makes "mistakes", the evolution process gradually fixes them.

References:

Sleep May Be Nature’s Time Management Tool. NYTimes.
Sleepiness and sleep-disordered breathing may be found in 19-29% of children with positive allergy test (http://goo.gl/AfCWZ).
Image source: Sleeping kitten. Wikipedia, Tilman Piesk, public domain.