Groups' use: access control, sharing (ie: private group) or both

Would like the ability to identify if a group is to be used for:

1) access control: as it currently implemented for access to custom forms, queues, etc

2) sharing: currently, all groups are available for objects sharing. Would like the ability to identify a group as private, so it is not available for sharing.

Note: the Proof product seems to have Private groups, per article https://support.workfront.com/hc/en-us/articles/115004086088-Private-Groups

Thanks