We use our external washer at some point every trip. If were at the beach it's for washing sand, if the dog finds roadkill to roll in, or just for washing up. I have a couple of plastic milk crates I keep in my passthrough storage to hold various items and they get turned over for the littleones to stand on and then one of those plastic mesh mats to let the water go through.
I guess i could live without it, but then I'd have to hood up a hose to the city water and it would always be cold.
FWIW, we have one in our boat and when its cold water crabbing season there is nothing like a little warm water to warm up cold hands after pulling pots.
2009 F350 CC LB 4WD
2017 Jayco 355MBQS