I agree there is no right way or wrong way for an owner to operate. It depends on the individual location,what they're willing to accept for the cycle time. If you are in a rural area, have a place to dispose of mud, and an employee on salary it can be to your financial benefit to allow mud washing. If you have no place to dump the mud, pay hourly for cleanup, and have more affluent clientele it might not make financial sense. It does seems to me more owners discourage mud washing than in previous years.
I have tried the "wash down when you're done" with customers for a while. It kinda works when I'm there, but the messes continued in the evening or night, so I've just banned mud washing outright. I have one sign, all inclusive at the point of purchase than prohibits mud washing and a few other activities.
There is something called the pareto principle, also known as 80-20 rule, that I think applies to some segments of carwashing. 80% of my mess comes from 20% of my customers. My personal decision is their mess is not worth their money, so I try to encourage them to use other facilities.
During hunting season, I shut my SS bays off on Sunday night about an hour after sunset. The place is dead by then, and that's when the hunters were coming in and trashing the place. I guess they have changed their wash habits, because I deal with mud much less than I did previously.