As per technet site the 'Overwrite' value for UpdateVersions parameter does following : "Overwrite to overwrite the current file and all of its versions (delete then insert)". But my question is does it delete all the items and replaces it with source items or it only deletes conflicting items? while running import command in verbose mode I found out it writes "deleting.." for every item. Isn't it a bad way from perfomance point of view to delete all the items and replace with items from source even if they are same?? Could someone share any good article explaining its internal working.