I had a job during medical school where I worked as needed (and when it was convenient for me). Before medical school I worked as an EMT in an ED. When school started I became a "pool' employee, with no real shift obligations besides a couple a year, but I could pick up as much as I wanted to. I also taught CPR a couple times per year.
My situation was rare; there was only one other person in my class of ~200 that worked (and she used to be a radiology tech).
I agree, there is a lot of other med school related things to do in place of working and in the grand scheme of things the extra cash doesn't mean that much.
However, I enjoyed my part-time job in healthcare because it allowed me to continue to have meaningful clinical experiences during my first two years of medical school as well as earn some extra cash (over the 4 years of medical school, I probably made around $5000, which definitely came in handy as extra spending money). The continued dedication to EM and EM related education also looked good when I was applying for EM residencies.
-senior medical student (T 45 days)