We always use a pen if we are staying more than a day in a Cg and haven't had an issue. We have two small dogs and they know that the pen is the spot to "go" which makes it easy for us to clean up. It keeps our dogs safe from other dogs that snap a leash and attack them. It allows them the freedom to wander within the pen while we sit in our chairs and relax. We also enclose our steps so our two cats can come in and out of the RV. The cats are leash trained but neither is fond of strangers so I prefer to have the leash on them and the door open so they can scoot inside when they need to. The pen stops them from going underneath the rv and slipping away after a squirrel.
Personally I feel that someone who goes to the trouble of penning their dogs are very responsible and they are ensureing that their dogs leashes don't scrape up the ground or local flora and fauna. Much easier to ensure all is scooped because its in one spot and it allows the zoo to stay with the family.
Any CG that says no to a pen we do follow their rules but we try to avoid those cgs.
We have travelled since 04 with 2 cats and 2 small dogs. Our zoo travels loose in our pickup and we learned the hard way not to leave the vehicle parked with the ac on. It was lucky I was in the veh when my cat decided to chase a fly out the drivers window and hit the window button. I was able to grab her before she escaped. We do have crates in the veh and now if its a short stop we put the cats in the crate and the dogs are ok as they are clipped on seatbelts. If its a longer stop we pack everyone back to the 5th wheel and let them wander in there with their litter box and food and water. Works well for us.