We have spent 36 nights at Wal-Marts since we went full time in 2007. If we are traveling from Point A to Point B on our way to Point C, we will typically pull into a WalMart for the night. In my opinion it makes more sense for us to pull into a Walmart to restock our supplies on our way to Point C. We don't have to unhook the toad to drive to a store, we don't disturb the rest of a campground when we pull in later in the evening and then again when we leave early in the morning. Not every situation is the same.
In fact, one of the best stories that our grandsons remember from a three week trip to Yellowstone was spending the night in a WalMart in Montana. It is a cuter story when a 7 year old tells it to his Mom over the phone call back home but it goes something like this -
Everybody got to get whatever they wanted at the deli for dinner and it was only $20! Then we got hiking sticks and new hiking shoes and snacks and flashlights and matching ball caps, and everything! And we got a movie from the Redbox that we can watch in the parking lot. And Mom, we're getting donuts in the morning!