TUT5124 Updating to GW2014 Convert Ext.Entities to Users

Hi all,
my customer converted already some time ago all eDirectory users to external entities as a preparation to be able to run his GroupWise system without eDirectory with the actual GW12.03 patch level
Now we have this recommendation in the 3rd slide of the TUT5124 presentation of the BS2014 where it is recommended to convert the external entities to eDirectory users as preparation step for the upgrade to GW2014.
Do we have some kind of technical background information why this step is required?
The customer reported that he was able to associate the external entity to the active directory user without problems, without eDirectory user.
Please advice...
Many thanks in advance and best regards,

Stefano Barello - Lanworks IT engineering