If you already have an XCF that already has links to codes in IR-specific devices, then you add the IR-specific devices to "My Database" the existing links still point to the old IR-specific devices. It's not like the existing links are automatically changed to use the entries in the "My Database". Thus, for existing configurations that already use the IR-specific devices, I don't see much use for "My Database", unless, as Dave said, you plan on creating other configurations in the future that can use the "My Database" codes.