I'm just on the edge of being a millennial. Been working since I was 12. Took freshmen year of college off from working because I was worried about maintaining my scholarship's gpa but worked in the school's post office and daycare other years. Was in a sports team, so saved the "lunch money" provided by the school during away meets. Interned for major-related work senior year. Worked for non-profits during the summers-- 40 hours plus. Even sold knives for a bit. Graduated with 10k in pocket and a car that I paid 5k out of pocket (stupid, could have gone cheaper). No, I didn't live at home; the full ride was really key.
I see some people here saying it's possible to graduate with no debt just by working and I don't know. I think it really depends on the school. Tuition at my private school was about 40k a year; it's now 65k a year. I don't think I would have been able to pay all that by working without jeopardizing my grades (even more, lol).
For grad school, I was already working full-time in my field so paid half tuition every semester and then paid everything off 6 months after completion.
I agree that working while in college show grit/organization, etc but I see plenty of people who do well having never worked (In one of my freshman seminar, I found out I was the only one who worked before college) while in college. I feel like they have more of an ability to focus in general while people who worked while in college are good at juggling.