I think it's complicated-- what kinds of challenge are good for people, and how do you judge how much challenge of a particular type is good, and for whom?

So far as I know, being low on sleep is bad for people. Um, except that sometimes modest amounts of sleep deprivation (like an all-nighter, I think) can raise energy. Again, vague impression, but some missed sleep can work as a useful reset for some people with depression, or set off mania for people with bipolar.