Vantaggi
It wasn't the worst job that I ever had. My coworkers and the managers were nice enough, the pay wasn't terrible, and the majority of the customers were polite. Once in a while you'll deal with someone rude or a downright creep, but you'll have that with any customer service job. As for the pace, it ebbs and flows. During meal times there's a big rush of customers getting last minute items, and they tend to peter out over the next couple of hours until the store is almost dead. Then as the next mealtime approaches, it rises again. In short, expect about an hour of excitement, gradually slowing down over the next hour, then 2-3 of silence.
Svantaggi
My experience (not everyone may have had it) was that I was often called in only 3-9 hours a week, and was often sent home early because of a dead store.