The use case for this is as follows:
1. We have a certain subset of users who need the ability to add/remove members of specific groups ONLY.
2. These users should not have permission to modify any other groups other than ones where they have explicitly been granted modify permission.

You may wish to restrict this even further so that users could be granted:
1. Add
2. Remove
3. Add+Remove

permissions for each group.
This would be extremely useful for us, particularly if those users could then add/remove members using the REST API. Secure automation ahoy!