You have computers that have not communicated in a specified amount of time and are looking for an automated way to clean these up.
Note: Purging works on managed computers that had the Symantec Manage Agent (SMA) installed only.
For information on cleaning up computers that came in through Active Directory Import but never had the SMA installed, see How does the Active Directory Import Synchronization work?
The Purging Maintenance in the console is located at Settings > Notification Server > Purging Maintenance > Purging Maintenance (on the left of the page that loads).
You can also access Purging Maintenance in Settings > All Settings > Notification Server > Purging Maintenance
See the bottom section, "Purge computers managed by this NS, which have not reported data for:"
You can retire and or delete computers based on your needs. Retire will set the computer to the non-active status of "Retired", and the delete option will remove the computer from the database.
if a computer comes back online with the agent still installed, when it checks in again the computer will be changed to "Active" if it is retired, and it will be recreated in the database if it was deleted.