Less cans in some cases means more of a mess. It depends on where you are located and what concept the customer has about trash and littering.
I have lids that are locked onto the cans (55gal) with a hole about the size of a coffee mug, obviously enough for "regular" car garbage, but not any other type of trash.
Once they fill the can, they proceed to dump their trash anywhere and everywhere. They feel they have the right to do it no matter what.
Time and time again, customers feel that whatever fits in their car is "on the list" as car wash trash.
That said, having some kind of lid that restricts how much trash can be stuffed into the can all at once does help in the long run.
Before I had the lids, the cans were wide open. That was when it was a free for all with tons of house garbage. The lids definitely cut down on the house “bagged” garbage. Now, I still get every now and then a customer who breaks open their house garbage and disposes it one piece at a time.