Depending on how the group administration has setup their group, a follower has the ability to peek into the inner workings of the group in order to decide if they want to take the major step of putting that group into the "10 besties" list. It's a sort of "try before you buy" or test drive for a group. Many people join a group and then don't participate. This gives them the ability to make sure that they are going to participate and be a contributing member of a group before they join. Following also means that if that group has something of interest to you, but you can't join (like those who are constantly stalking HFCS) by following, they will get notified of public, shared or other content directed at group followers.