I've never belonged to an occult group, and only briefly considered joining two, before I determined that I'd rather just pursue my own path. But recently on Facebook someone revived the Zee List and for a time I participated on that list way back when and it was interesting to observe how different people responded to the revival of the list in a different forum. The desire to belong is a current that seems to run strong in general in occultism and the forms it takes, whether it's a virtual community such as the Zee list or the more formal organizations such as the OTO or Golden Dawn. The desire to belong isn't the only reason someone will join an occult group, but I think it's fair to say it's a major reason people join. It's not a bad reason to join either, but it is an interesting one, because so much of the occult memes about being on the fringe. At the same time, it's natural that people will want to group together based on similar interests.
I never joined an occult group or lodge because I've always preferred my independence. Even with the zee list, which was never a formal group, it was more about sharing experiments, than actually being part of the group. My experiences with occult lodges in passing has been mostly negative, but I'm always open to the idea that someday I could change my mind. But I don't think belonging to an occult group is an absolute essential. It's something many occultists do, but its equally possible to focus on your own studies or getting together with friends to discuss experiments without necessarily making it into a group organization.