We've found that as a family, being able to stop when and where we like during the day (to see the sights on the way), and stopping for a nap when tired, puts us pretty far behind schedule. The answer? Fill up at a truck stop when we're tired at night, pull to the parking area 60 seconds away, and sleep. I'd much rather spend the extra daytime hours seeing interesting places than scurrying to a campground that looks just like every other campground on the road.
In the morning, we have a quick breakfast (dry cereal or such) and we're back on the road, well rested.
The only issues at a truck stop or rest area can be the noise of big trucks or other RVs pulling in, especially in the summer when you need the windows open for ventilation.
I haven't had any problems at Walmart or other big box stores either, in the back 40 of their parking lots, but Walmarts annoy me, and oftentimes these stores aren't quite as conveniently located off of our travel path.