Your connection sequence is batteries to controller then array to controller. So you don't want to disconnect from batts with the array still on the controller. Covering the panel would be a good way to switch off solar. I put a switch on one of the wires from the panel close to the controller but my controller is easy to get at for that.
Useful if you are disconnecting the batteries for various reasons, you can turn off the solar first on the array side. Also with the array wire "open" you can measure Isc and Voc if you like.