I don't know how to answer this from a security perspective, as any group you create is only as secure your system's file permissions. From an purly administrative perspective, make common groups. 1) they are easier to work with. 2) if you don't, and have a couple hundred users, you'll end up having a couple hundred groups, all named after each user.
It seems that RH defaults to this activity of creating a group based upon the user's name. Personally I find it rather annoying.