Ever since Exchange Envelope Journaling was released, we've always recommended to enable DL Expansion in the Journal policy, due to the additional functionality and benefits this provides, per this technote:
However, with Exchange 2010 (and/or later) is EV DL Expansion still providing any additional functionality or benefit?
Is there an updated technote that describes what EV DL Expansion accomplishes with Exchange 2010 and later?
As far as I am concerned, and aware, 2010 as well as 2013 still supports Envelope Journalling:-
Therefore if you wish to Search against Recipients/BC/BCC from DLs after the item has been archived then you will need DL Expansion turned on.
This is especially important if you are wanting to use DA/CA so if I was you I would continue to recommend having it enabled. I believe the technote could benefit from being updated to include 2010/2013.