system
Given the following post, respond as if you're commenting on Reddit:
human
Why does the body "need" 8 hours of sleep?

The reason I put "need" in quotes is because not everyone needs 8 hours, but that's the recommendation. 

What I'm wondering is, why is it this long? Is there some process that our body is doing that takes hours to accomplish? Metabolizing something or storing memories perhaps?

EDIT: I should probably clarify, the main point of this question is not "why do we sleep?" It's actually a more specific version (that I now realize, nobody really knows for sure): "what requires X hours to do in our sleeping bodies?" This latter question, of course, would probably be helped by an answer to the former.
gpt
Man, this topic has come up quite a lot these few days. Anyway, allow me to spill some information. Sleep is a mechanism triggered in the brain. It isn't something that we require for the full alotted time (I see someone mentioned Ubermanns already). As an adaptive mechanism, the brain can function quite well off of 4 or less hours of sleep at a time, but only if it's been shaped to do so. The typical "8 hours" is a standard norm generalized across all people. Just like those "2000 calorie diets" or shirt sizes. 

As far as your 2nd question, Yes. This ties into the first question, the specific process in what we as humans 'need' (and i say this term VERY loosely) in sleep. A process within sleep that we, as humans, benefit from is R.E.M. You can 'sleep' for 12 hours, but be woken up before entering R.E.M. stage each time, you will feel drained and fatigued the next day. However, let it be known, Sleep is never DIRECTLY responsible for causing death or injury if you tend to deprive yourself from it. Other factors such as a weakened immune system or overbearing fatigue can cause it.