I read an article many years ago, by a man who was working 80 hour weeks. He analyzed his work and tried to optimize it.

Eventually he cut his working hours in half, while actually doubling his output, because the shorter work hours required him to actually focus.

He was, of course, self-employed, and could design his work week how he liked.

I guess that's important for another reason: if someone else had been paying him by the hour, he would have experienced a 50% pay cut. Instead, his income doubled, because it was based on the actual results.