I know what you asked, I can read 
With enhanced security, individual user permissions to tables are pushed down to SQL Server, so that this is also enforced on connections to the database other than NAV connections. It is never used by NAV though, because security in NAV is done through the application role and set up inside the app. The only thing that the enhanced security model does for NAV is slow down the synchronization process, there is no added benefit for NAV. If you need external access to the NAV database, I always recommend setting up additional users for that specific purpose.