Well, kind of like H&R Block Income Tax service. After they calculate your tax return information they offer you their "Peace of mind" protection in the event of certain events, H&R Block will make changes to your return or represent you with the IRS. It's "peace of mind" knowing you do not have to face an unpleasant experience (should that ever happen) alone.
RV power protectors are kind of like that H&R Block "peace of mind" service. You may never need it. No one ever expects to get an audit by the IRS, and most of us never do. Most of use never experience electrical problems at campgrounds, or even plugged in at home. But, there is alwasy that one exception, that one time! That's when "peace of mind" is priceless!
I do know, I keep my camper plugged in 24x7x365 at home when not on the road. I keep the protector plugged in. Many times we have experienced the lights flicker, lights go dim, and lights brighten up. We have had lightning strikes that have taken out our internet antenna (we have a weird service at home), and even our interne router. We've never had an appliance get fried because of lightning strikes, but our internet equipment has. So at home, the RV power protector is doing it's job. I have "peace of mind." Otherwise, I'd plug in the camper ONLY when actually using it.