One reason to have 12 volts is those long treks thru empty places.
Traveling the Trans Labrador Highway, one day we did a 200 mile stretch seeing only 8 other vehicles in over 7 hours. We averaged under 30 mph on that day.
Obviously we had to stop for an occasional pit stop, lunch stop and lets stop and check out the neighborhood (though no neighbors). On those occasions it was nice to have 12 volt power or AC by turning on the Inverter, possible because we had a battery
We did carry a small generator
on this trip because one never knows what will happen when you're far from normal civilization. However, when you stop for lunch you typically don't want to crank up the generator
A 12 volt system is worthwhile. Really the only penalty is the battery
and the converter. Of course I feel the same way about a propane
system. The magic of these three way systems is choice and backup.
Traveling through the wilds of the world does mean you may have to be truly self sufficient. When we're really away we carry things we would never consider for normal RVing, backing up the backup....