Pros
As a graduate student, having the TA job is really helpful since I don't work outside of this job and my classes. A major benefit for me is having the health insurance covered by the school, since that can be quite expensive. The hours are flexible, so I do my work on my own time for the class I TA for. You get some experience teaching and tutoring students outside of class as well.
Cons
I wasn't sure whether the insurance information would be different from semester to semester, so I had to purchase the student plan to remove the registration hold. Then I had to get a refund for the student plan since I was on the employee plan as a TA. This is only a possible con for students since the TA position isn't really finalized until after the new semester starts, and registration occurs at the end of the previous semester.