Time off doesn't really enable anyone to work a different schedule, as mentioned above. If your boss wants 40hrs/week and you want to work 30hrs/week, you’ll burn two weeks of time off in 8 weeks.

I'm referring to long term time off like reduced schedules due to family, personal, or medical hardships. I've worked with dozens of people who worked reduced schedules for years of their careers for many various personal, medical and family reasons. It's actually much more common than you expect.

I have worked with many people who do the same as well. You can do it if you're in a privileged job, like many of us work, or if you were hired under those circumstances. If you have a below-median wage job where you're expected to work 40hrs/week and you have a medical hardship, you'll be looking at being reassigned to a part-time position at best, and if one is not available, you'll be spending your FMLA time looking for a new job.