The major reason for me when parked is to keep my battery bank charged up all the time. If flipping the DISCONNECT switch prevents the on-board converter/charger from charging the batteries then I would not do this in my case...
I have always thought the battery load for the on-board converter/charger units is very helpful for the converter/charger DC output regulation.
Some of the older RV UNITS actually had a battery check circuit and will shut down the on-board converter/charger if the battery has failed.
Of course the newer converter/charger units are better built and does not need the battery load to insure proper DC regulation but having a constant battery load is not going to hurt things.
Roy Ken