I am finishing up my 2nd year of physical therapy school and, from a personal standpoint, I am glad to have never worked throughout grad school. That being said, there are a couple classmates that still hold part-time jobs but only work on Saturdays and others that got hired through my school to help give tours, answer emails about the program, etc. for a couple hours per week. It is entirely possible to work part-time and go to school, but I prefer to think of school as my job, and I'd rather put my full effort into it rather than split it with another responsibility. The weekends are also both my most productive days, as well as my day to recharge for the next week.
You should ask yourself what the cost-benefit of working part-time is. Is the small influx of cash worth losing 4-10 hours per week that you could hang out with friends, catch up on studying or get some extra sleep in. That's my two cents.