Well, my experience in inviting people occurred before that innovation was introduced. If I were inviting a relative today, I think it would make sense for me to be able to assign them a couple of tags to get them started -- and tell them about the tags in my invitational email. That's because I already know something about these people and their interests, or I wouldn't be inviting them.
As a general rule, I think that a personal note from a known cousin is a friendlier greeting than a generic greeting message from a stranger, and should be more effective. Additionally, note that invitees who remain as Family Members often are relatives who only expressed an interest in seeing the private content on family-member profiles, and are not interesting in being invited to join a project or sign up for email notifications about edits for their surname.