When this option is set to Yes and you are restoring a server that does not currently exist on the system, the Unix user and group IDs for the server administrator and mail/FTP users will be re-allocated to use free IDs on your system. This is typically what you want as it avoids clashes with existing IDs on your system.

Selecting No tells Virtualmin to use the IDs that were in use when the backup was created. This should be used if other files still exist on the system with the old IDs, and if those IDs have not been allocated to any other users or groups since the backup was made.