This is technically called IFM (Install from Media), this is useful in case we have a domain and we want to expand it with more domain controllers and we do not want the Active Directory to copy us over the network to the new domain controller, For example, if what we are doing is a domain controller in a delegation that its Internet bandwidth to where the primary domain controller is is quite loose, copying the Active Directory database may take a couple of hours or more copying it. This is used for this purpose:, the system state of the primary domain controller is backed up and restored to the one we want to be an additional domain controller in a directory, and when joining it to the domain we use this restored data instead of replicating the AD.