Pros
As a part time instructor, the flexibility in scheduling was a huge advantage. I was able to balance work and school very easily, and the managers at my center understood the importance of my school schedule. The salary was certainly a major draw as well. Very few places that a college student or medical student can earn that much part time.
Cons
Schedule wise, you are at the mercy of when classes are available. I taught mainly MCAT coursework, and at the time, there was only 2 administrations of that exam during the year, so there were periods of time where there were either no classes or only one or two, which made it difficult to get hours. Of course on the flipside, that also meant as we approached those two dates, there were lots of classes and I was constantly bombarded with requests to fill classes.