Facebook has released a new update which adds some new parameters around how group admins are able to invite and add new members to their groups.
Up until now, Facebook users have been able to add friends to groups which they believe those people will be interested in, and those friends would automatically be added to said group. You've likely experienced this for yourself - you get a notification that you've been added to a group of some kind, then you see a range of group updates making their way into your News Feed.
This can be a good way for group admins to inflate the size of their groups, because while those added users can, of course, remove themselves from the group, friends, in particular, may simply mute notifications, so as to not cause offense, but filter the updates out of their feed.
As Facebook notes, this also means that there may well be people who've been added to your group who've never actually visited it. So now, these users will not be automatically added, but will be put onto a new 'Invited' list in the group admin dashboard. If a user is invited by a friend, they'll need to manually accept that invitation by visiting the group. They'll also no longer be included in the total group member count, which could see some group audience figures drop.
Facebook is also giving admins the capacity to send one reminder note to each invitee to re-prompt them to join their group. If those users don't take action, they won't be added, or listed in group member counts.
It's a fairly simple, and logical addition for Facebook - as noted, it can be annoying to be added into a group, and to have your News Feed invaded by random updates from discussions that you may actually have little to no interest in. But it will, as noted, affect some group member counts. If you've invited a heap of people to join your Facebook group, and you haven't seen those people active in your community, you could see your numbers decline.
The changes are going into effect over the next few weeks.