Ventajas
the pay is more than enough to support yourself as a graduate student and health insurance is included, and while the amount of time devoted to the position per week can vary, on average you will devote fewer than 20 hours per week to the position
Desventajas
The workload can vary greatly based on the course you are assigned and the professor teaching the course. The majority of my TA assignments were positive as professors were organized and had reasonable expectations for TAs. However, I had two extremely negative experiences where the professors were completely disorganized to the extent that as a TA I needed to try and impose structure on the course and clarify the professor's ambiguous assignments and "suggest" extensive modifications to ill conceived syllabi, which is an awkward position to be in as a TA. If the university or departments could provide guidelines on how to handle such situations it might be helpful, although I have the sense that nothing can/will be done as both professors are notorious for their disorganization and poor teaching quality within the department.