Lama Ole’s answer:
Basically, sleep is ignorance. But it is also a very useful ignorance. If you haven’t slept for too long, then you put the firecracker into your mouth instead of the cigar, like the joke about the drunk on New Year’s Eve.
If one needs very little sleep, then one might have a slightly manic predisposition. One does everything too quickly and then has many ups and downs. Despite the many great yogi examples like Milarepa, who hardly slept for a very long time, my experience is that one depletes one’s own reserves.
I myself am known for sleeping little. For weeks, I can function with three to four hours of sleep per night, but then I really lack something. If I get less than five hours per night for a week, then I sit there and know exactly what I want to say, but my vocabulary shrinks from fifty thousand words to five thousand. If you want to learn more, to really enrich things, and above all to work intellectually with words, you actually need six to seven hours of sleep per night in the long run. Otherwise you may achieve quantity but not necessarily quality—I have noticed this while writing books. The same holds for a body that is active, that loves, that jumps, that does things, that thinks, that usually doesn’t go to bed before three o’clock in the morning. Only those who stay in one place for a long time and don’t do much mental work can really reduce their need for sleep.
You are lucky if you manage to go to bed early from time to time—preferably before midnight. I myself have done this a few times during our book retreats. The dream phases one can go through then are pure luxury! But one shouldn’t sleep too much either.