Vantaggi
You get to watch movies for free with one extra person, and you could get discounts on concession products. Also, the branch that I worked at had contests on whoever could sell the most products and the winner usually gets free food/candy/movie tickets/etc. Plus it's a great way to meet a lot of people your age if you're a high school or college student. Also, there are free screenings of movies that haven't even come out yet for employees and their families.
Svantaggi
It's usually a minimum wage job, so money could be an issue. Also, the hours are not stable. You could work up to 40 hours in one week and only 5 hours in another week. And I really did not like on-call days because it was hard to plan things. Plus if you work at the movie theaters then you may as well say good-bye to your weekends.