Q. If I remove a Group Policy preference, will the changes it made be undone and the pre-preference values restored?

A. Normal Group Policy settings are written to special areas of the registry reserved for policies, which means the original value isn't overwritten. Because the old values are still available, Group Policy settings don't tattoo the system—when the policy is removed, the original setting for the user or machine is restored.

Group Policy preferences don't write to special preference areas of the system and instead write to normal application and system areas. When a preference is removed, the values that were set before the preference was configured won't be restored, because the original settings have been overwritten. Group Policy preferences do tattoo the system, because even after you remove the preference its changes are still there.