Pros
If you're actually able to get the Graduate Teaching Assistant title, the benefits are extremely good for students and I would highly recommend it, especially if you can work with a professor you gel with.
Cons
Some departments will employ both graduate and undergraduate students as "Learning Assistants", which have similar duties to Teaching assistant but who get paid less than 20% of the TA counterparts after the consider benefits. It's essentially a grift that they do because they can get away with it. I was even asked to LA for a class I had TAed for in a previous semester. When I refused, they made me a TA immediately. That made it clear to me that they were just trying to take as much advantage of me as possible, and when it became clear that I wasn't going to do the work for so little they capitulated right away because they wanted me to help teach the class.