If I worked less, I'd want to spend the extra free time doing something important. The problem is, I don't think there's anything I could spend my time on that would be (a) more important than my normal work and (b) at least as likely to succeed as my normal work. I'm much more likely to do something I can be proud of if I put all of my time into one project rather than splitting it between several different projects.

If work is just a thing you do for money, then minimizing the amount of time you spend doing it makes sense. If you actually find work satisfying and care about the results, then I think it often makes sense to devote as much time as possible without causing yourself to stop enjoying it or become unproductive.

Having said that, I do try to reserve some time for side projects because that's a good way to develop new skills that I can apply to my main project.