What is the 'Quest Diagnostic Server Read-Only Users' group?
The new Quest Diagnostic Read-Only User Group enables organizations to limit access to Spotlight on SQL Server (to read-only access) to specific users. These users can view the home page and drilldowns for connections but cannot make changes to impact Spotlight's operation.
So basically, you add a domain user to that group, and they can log in, and see (view) everything, but they cannot touch (change any preferences, kill sessions) anything that would make a change to the app, or session. They cannot change the Diagnostic Server or any Monitored Servers.