Yep same situation with my boat. I have dual batteries with a switch. One for starting, one for "house" use. Don't wanna be 10-20 miles from the dock with no battery to start that big engine!
Although I have an 8hp honda trolling motor that can pull start, it would take a long time to get anyplace with that little bugger!
The selector switch is a different issue from charging.
You are correct in that they are a good thing to have for the
reason you mentioned.
No reason one cant be installed on a truck also so that the starting battery can be isolated.
