Use Cases:
1. Major or Minor Announcements
2. Sharing Files
3. Discussion Forums
Report can be used to check the adoption. Check the following steps:
1. Create a Report on “Collaboration Group Feed Posts Report” Report Type.
2. Group the Report by Group Name and use Record Count column to find the Posts Count in the Chatter Groups.
For more tips, check the Chatter Group – https://success.salesforce.com/featuredGroupDetail?id=a1z30000006IDZHAA4