I've tried to drive to my campsite when folks have tried to cram vehicles that were too big for the pad. The road is barely one car width with trees and boulders right at the edge. And then I have to try to get around the trucks that are sticking out into the road. That 4 inches can be the difference between a blocked road and a passable road.
I stayed at one campsite last year. It's identified as fitting a 25ft TT or MH. I had stayed at it several years back with my 20ft TT and it was fine - I actually fit my TT, Durango and a friend's chinook.
This time, I brought my FnR - which is 16ft with tongue. I barely fit it and the Durango and had to park the Durango sideways to keep it out of the road. No way would the chinook have fit this time.
Why the difference? Because before, the pad was laid out in such a way that folks couldn't back into the site easily. It required a sharper turning while backing in and folks had difficulty. Since then, they moved it so it was easier to back into, but that put the tree directly behind the pad and created such an angle between the front of the pad and the road that you lose a couple feet on the road side of the pad due to the road turning. Had I pulled the Durango straight in this time, its nose would have stuck out right at the turn, blocking folks with anything but a small car from being able to make the turn.