Of course while taking short breaks to keep your mind fresh is important, actually making sure that you get enough sleep each night is absolutely essential. Why? For lots of reasons, such as:

The brain can process complex information even while asleep, thereby preparing you for action upon awakening
The brain consolidates memories during sleep. Consistent lack of sleep can adversely affect recollection
Sleep can boost the brain's creativity - researchers at the University of California linked sleep with the brain suddenly coming up with those "a-ha" moments!
Sleep helps protect the brain by giving it a chance to clear out potentially harmful toxins.