Pros
Working closely with professors allows you to absorb their knowledge. Opportunities to network with professors and others in academia and in industry. Flexible schedule to allow for time for research. Use this as an opportunity to learn a real skill or tool to put on your resume to make it easy to find a job in the future. Use this part-time position to work on your research or do an internship to gain real world experience. Some weeks you may only do a few hours of the professor's research and other times you are working very hard to help them to make their deadline and putting in time after hours. It all comes out evenly in the end.
Cons
Contract is only good for 1 semester and the professor must invite you to renew it each semester. If professor is no longer funded, you may be out of a job unless you jump on to another professor's grant. Flexible schedule means you work on professor's schedule and timetable; some weeks you may only do a few hours of the professor's research and other times you are working very hard to help them to make their deadline and putting in time after hours.
