It is nice to have an adjustable charger input. Since we have 400 watts of solar I can set it to 0 or 5 amps when plugged in on shore power. I can keep my carbon foot print a little lower
It is useful when on a weak 30 amp shore power. The batteries will charge fine at 10 amp input (if you are in one spot for a while) and will give you more power to run other items without the ems kicking in. Also keeping it on a lower setting will exercise your batteries a bit more. I like to play with all of my systems, if you don't leave it at 25 and call it good.
I have done the same as Jeff when I tried to run off of the honda 1000.