Enrolment

After some initial experimentation with IMS Enterprise we decided to go with LDAP (for authentication) and External DB (for authorization, i.e. enrollment). Still, I wonder if people would like to share their perceptions about the following observation.

If you use External DB for enrollment then Moodle essentially is sharing the very same data with the backend SIS, although it may make an operational copy of its own in MySQL. On the other hand, IMS Enterprise requires the creation of a file that duplicates (part of) the ERP database, and then Moodle creates yet a third copy of the data (in MySQL). If file creation or cron updating of MySQL fails for whatever reason, the data are not synchronized.
These would seem to be two very different approaches!

Ditto for using LDAP for authentication as opposed to IMS upload of user data from the backend to Moodle. In one case authentication is actually shared at run-time (although it may be synch'd ahead of time) whereas in the IMS case you are duplicating data and then authenticating against the copy.

So: what advantages are there to IMS, if we do have LDAP and External DB plugins capable of implementing a "tighter" integration? One thing might be an extraordinarily large dataset that chokes LDAP on the synchronization. Perhaps another would be intermittent failures of connectivity with the LDAP server or external DB server.

Are there other considerations that could motivate in favor of IMS ?