Creating wp users without usermeta data

I’m working on a plugin that creates users in the wp_user table, with the option to do batch imports of users from another location. User-specific data is stored in a non-WP table in the same database (so, not in the wp_usermeta table).

I notice that WordPress automatically creates a wp_capabilities entry in the wp_usermeta table for new users that defines permissions. How will WordPress handle user’s who login, but who do not have a wp_capabilities entry in wp_usermeta? Does anyone know?

Thanks!