Define "need". Also, citation needed.
Just because you can get away with it and live, doesn't mean it's the best move.
“In 2009, a woman came into Ying-Hui Fu’s lab at the University of California, San Francisco, complaining that she always woke up too early. At first, Fu thought the woman was an extreme morning lark – a person who goes to bed early and wakes early. However, the woman explained that she actually went to bed around midnight and woke at 4am feeling completely alert. It was the same for several members of her family, she said.
Fu and her colleagues compared the genome of different family members. They discovered a tiny mutation in a gene called DEC2 that was present in those who were short-sleepers, but not in members of the family who had normal length sleep, nor in 250 unrelated volunteers.
When the team bred mice to express this same mutation, the rodents also slept less but performed just as well as regular mice when given physical and cognitive tasks.“
http://www.bbc.com/future/story/20150706-the-woman-who-barel...
For instance in the US today childhood injury and fatality rates have plummeted [1]. And this seems like an obviously good thing. And one might reasonably hypothesize that the increase in rules and regulations against letting children play independently, as well as the rise of helicopter parenting has played some substantial role in this. Since it's very easy to see the link there.
Yet at the same time other factors such such as childhood mental illness, obesity, and other major issues have sharply increased. Relative academic results are down and even IQ levels are declining. Are these linked to the behaviors that have driven the decrease in injuries in fatalities? Well that's a lot harder to say, though I think it's a very reasonable hypothesis that at least some of these issues are linked with the same behaviors that have reduced childhood injury/mortality rates.
This is a recurring pattern in many things. Our understanding of the causality of genetics right now is essentially 0 keeping in mind that saying gene A 'causes' effect B is no more a meaningful understanding of the reason for the causality there than saying rain clouds cause rain.
[1] - https://www.childtrends.org/?indicators=unintentional-injuri...
If you go long enough without needing to be on a schedule, studies have found a lot of people move back into a rolling/rotating sleep cycle .. a few hours at a time throughout the day/night. I found myself doing this while I took a several month sabbatical from the workforce.