the Laffer Curve? trickle down economics? something....something?? sorry, what was the question?
never touch questions on battery switches, but have some experts here. I tend to leave them on "both", which defeats one of the purposes (i.e., fish and play the stereo all day, then have a battery to start the motor). Can say, with a two bank system (with two batteries), "both" allows starting (and charges both). The setting doubles up the amp hours, but draws on both. Guessing, two parallel banks with two each in parallel would operate the same. "1" or "2" gives you two batteries, "both" gives you four. Wait for better advice (and a diagram or two). May want to post a thread over in electronics.
edit. "voodoo economics......"