The attached ladder won't slide on the ground or fall over sideways. If it's in good shape, I'd think it would tend to be a little safer than an extension ladder leaned against the RV. For maintenance at home, I use it to get on the roof partly for those reasons and partly because it's convenient when I need it.
When camping I see no reason to carry a ladder with me to get on the roof when I have one already attached to my motorhome. The space and weight can better be used for other things I probably don't need. It's surprisingly common to want to get on the roof for some reason or another when camping; I made excursions there in my last camping trip to apply awning repair tape (which had been mouldering on the todo list for a little too long, truth be told), to sweep off pine needles, and to remove a stick I noticed up there when stopped at a shopping center on the way home. As best as I could tell it must have come off a tree while at the campground and sat on the roof for a good many miles; I was actually rather glad it hadn't flown off and bonked someone else's windshield.
