At the moment, "Check for embedded item record data" in stage-marc-import.pl defaults to "Yes", but I doubt that the majority of libraries would want to check for embedded item record data. (By extension, I think it would be good to default "How to process items:" to "Ignore items" instead of "Always add items" - just to be on the safe side.)
I suppose since this would change existing behaviour, this would need a system preference...