A part time job heavily depends on each situation. I will outline some situations from best to worst:
1) Part time job that relates to major and is low demand (time wise or mentally). Absolutely do it and the experience will look great on your resume.
2) Part time job that relates to major but is high demand. Carefully consider how much time it is taking from your studies.
3) Part time job that doesn't relate to major and is low demand. Only if you need more money for tuition or require financial independence for other reasons.
4) Part time job that doesn't relate to major and is high demand. Don't do it, it's not worth it.
At the end of the day you know your situation best. Sometimes college is about making mistakes. Sometimes getting a job you hate makes you focus more on school. Sometimes a part time job that is mentally tiring can make you stronger and might have other tertiary effects. Remember what your goals are as well throughout this process. I.e. Want to go to grad school? The hit your GPA took from getting that part time job will hurt you disproportionately.
There's no absolute right or wrong answer, weigh the pros and cons. Good luck!