User blog comment:DaNASCAT/Introducing New Moderator Opportunities For Community Administration/@comment-1370845-20160113231734

Far as I can tell, this just means that if you have a custom user group that's very similar to Content Moderators, you can request to have the new group and replace your old one, or you can just leave it? Sometimes there are minor differences, like a similar group lacking the Delete and Protect button, or sometimes they're different entirely.