Pros
Flexible; many Professors working understand and graduate student workload and will try and work with you. Also flexible in what courses you can take for your major, as long as you advocate for yourself. If you get a good, thoughtful professor to teach for, for a subject you enjoy, it can actually be quite fun. But the chances of getting one isn’t in your favor, unfortunately.
Cons
Horrible work-life balance for most science graduate students. The professors expect 100+ hours a week in labs and will encourage you not to take your teaching assistant work “seriously” and do the bare minimum there. Meanwhile, some professors take no consideration for their teaching assistants and don’t do anything to try and help with the workload. Many times for no benefit to the undergraduate students whatsoever, entirely on time-wasting meetings where all serious issues are ignored and not dealt with in any way.