Having separate data for the Mac’s Address Book application and your Bento Address Book could lead to issues down the road, because the data could diverge if you forget to update one application or the other. To prevent this, Bento automatically uses the Mac’s Address Book data to populate its Address Book library.
This data connection is always active, so any changes made in one application will be immediately reflected in the other. Bento uses this same data connection for its iCal Events and iCal Tasks libraries.