Well one is for the separation of the cranking and the house bank the other is to separate my two house bank batts be casue my batt charger has priority charging and conditions each batt separately so for shore charging I have to separate them so it will read right. Also it's there so if I stop to party cove or radio on boat off for what ever reason and drain the two house batts down I can separate them so the acr won't switch back and forth so much when I first crank the boat back up and it also limits the demand placed on the alt. then when the voltage builds up in the start batt and one of the house batts I can add the second house battery back in and let it charge up as well hope all that makes since