Hello,
The option of "Delete clients that have not connected for __ days" would delete the clients which have not connected to the SEPM for "x" amount of days.
Configuring a low value for this setting would clear up the enteries more quickly.
It is important to consider clients that are offline over the weekend. Setting this value to 1 or 2 will likely cause all your clients to be removed after a weekend.
A recommended value for large enterprise environments would be 7 to 14 days.
In case, these machines are coming back on the network, in the Next Heartbeat Interval, these clients would get re-register with the SEPM.
Below is the information on -
Delete clients that have not connected for specified time. N days
Check to delete the clients that do not connect to this domain in the specified number of days. The default is 30 days.
Over time, the Symantec Endpoint Protection Manager database may accumulate entries for obsolete clients. Obsolete clients are the clients that no longer function in the environment. Clients can be made obsolete when operating systems are upgraded or when a computer ID is changed. Obsolete clients count against the product license, so it is important to purge obsolete clients quickly. If your license reports show more seats are licensed than known to be deployed, you should purge the database of obsolete clients. You can shorten the purge interval to purge more quickly and then reset the interval to suit your long-term needs after the purge cycle completes.
Delete non-persistent VDI clients that have not connected for specified time. N days
In non-persistent Virtual Desktop Infrastructures (VDIs), you can set a separate time period for the non-persistent clients that have not connected. This setting can be equal to but not greater than the time period for all clients. The default is 7 days. Use a period that is short enough to make sense in your virtual infrastructure. Symantec does not recommend that you use a long time period.
If this setting is not enabled, then non-persistent VDI clients age the same as all other clients.
Hope that helps!!