Ventajas
It's a good place to learn about customer service and restaurant work if that's something you're interested in, so it works as a first job. It's very easy to keep yourself busy there so your shift can go by quickly.
Desventajas
The training experience was rocky because I was trained by a different coworker each day (some coworkers are a lot worse than others) and they were often too busy to properly teach me how to do things, so I had to learn a lot of things on my own. The schedule changes each week so it's difficult to plan things and establish a routine in your life outside of work. The environment got really stressful when we were busy because there often weren't enough people to help out. They often tried to call me into work on days I wasn't scheduled because of that. You usually don't get a break at all if it's really busy. The stress alone is why I'll never return to a fast food job.