Save Over Current File (default) does not open the Save As dialog box. If you open either the original file or the edited copy, the first save overwrites the original (as do all subsequent saves in that edit session).
Always Ask opens the Save As dialog box the first time you edit and save the original file. All subsequent saves overwrite the previous version until you close the file and then reopen it to make further edits. If you open the edited copy, the first save opens the Save As dialog box.