70% of the articles and books I've read on sleep will say something like "Sleep is one of the big mysteries of biology" at least once. While it is not 100% understood, there is a lot that is known about the impressive health, fitness and anti-aging effects of sleep. Sleep is particularly important for memory, mental flexibility, creativity and the development of novel insights. If you're someone who's staying up to get more done, you may be sacrificing your chance at sparking that big idea that takes you to the next level. Even for the body, if you're aiming to gain muscle or just sleep, you're shooting yourself in the foot by not getting enough sleep.
If this topic was interesting for you, I recommend checking out these books:
-David Randall's "Dreamland" (http://amzn.to/2kxuYij)
-Shawn Stevenson's "Sleep Smarter" (http://amzn.to/2jHS7Op)
-Arianna Huffington's "The Sleep Revolution" (http://amzn.to/2kdtjRx)
Dreamland was the most interesting read and Sleep Smarter had the most actionable and practical advice with a decent amount of science. Sleep Revolution was a bit bland, the stats and facts got old and the science part didn't cover as much as I hoped. However it did have an effect on my attitude about sleep so I will say it was worth reading.