I think there's a happy medium. I have a personal target of 4 days/week (or equivalent), and so I don't mind optimizing existing work, and then taking on additional work, as long as it averages out to this healthy balance. I have found that the best motivator for me is a manager who is able to say "you've done great work, you can relax for a bit, take some time off". I'll work hard for them, knowing they have my back and I don't have to fight and scrape for well-deserved rest. If they won't say that, and will just let me work as much as I can, then I start making clear boundaries around my work; and overall I am less motivated to make things better.