I was surprised to find an outside shower on my MH as well, and have yet to figure out any scenario where I would want to use it.
I've even thought about unplumbing it and capping the lines and filling the compartment with insulation panels. Of course, the least effort thing to do is just leave it alone.
Plus, it's on the driver's side, and locked. I don't usually carry the MH keys (about 50 gazillion of them) on me, so first I would have to walk to the entry side, get the keys from the hook inside the door, walk around, unlock the shower, use it for some unknown reason, lock it back up, then go put the keys up. And I'm sure my feet would get dirty again with all that having to walk around the rig.
*shrugs* Supposedly it makes the NADA value a tiny bit higher.
By all means, if you want one, go for it! I imagine if I had kids and were at a beach, it might be useful.
good luck,
jim