It always works out well when you really get along with the people in your groups. However, there does need to be some ground rules set before you begin working with someone you already know. Part of working in a group means sometimes you might not agree on everything, but keeping things professional and being flexible are a good way to alleviate any tension between group members. It’s important to not take things too personally and treat your work with a certain level of professionalism. Ultimately, I would say that it’s nice to work with people you get along with, but you also need to make sure that those people are willing to put in the work.