Taking one battery away to recharge it in the sun while the other still runs the rig in the shade is an advantage for sure.
A variation of that is if you have a gen in the truck or you have alternator charging in the back you can recharge the one battery some while driving around doing tourist things or whatever away from the rig.
For long term off-grid and it is time to run a full recharge and then an equalize on solar, a split bank like that lets you do that too. You can't get that done while there is a draw on the bank as there would be with both batts working.
