Rick, we leave it on all the time, keeps battery charged. Unless your going to store unit someplace without power hooked up for a long time. Then we would turned it off to stop the parasite load from TV, Microwave, clocks that would drain it over a period of time.
Ken, You will not find one on your Bighorn, unless you installed it and just forgot where you put it. Bighorns do not come with a battery cutoff. I did put one on mine, but never use it unless I am going to playing with the circuits and don't want a surprise spark. It is easier than disconnecting cable from battery.
Jim M