A 3-day work week would give rise to doing 2 non-concurrent jobs, or a six day work week.
I mean, I could see the benefits - don't like one of your jobs? Quit one, it isn't loosing your whole paycheck. Of course, there are weird structural problems like getting scheduled for those 3 days and random times throughout the week making it really a 7-day job with only 3-days of work, and the whole "you can only work 19.95 hrs and if you work more, then we are required to give you health insurance, so you can't work more than that."