Okay... A different view from me. I come from NE PA. Typically I will leave a night after work to get down below the DC Beltway then pull over. Then drive almost all the way the next day, pull over for the night and then pull into the Fort the next morning. I typically don't stay in campgrounds along the way. I use Truck stops or Rest Stops because my stops are relatively short (6 hours or so). Others have stated concerns about crimes at rest stops or legal concerns as far as how long you can stay at a particular rest stop. As of yet, I have not had any issues personally with my travels. From what I have read most states (LEOs) will generally leave you alone unless they feel that you are boon-docking. If however, you are just sleeping to drive your next leg safely, it seems like they will leave you alone.
It's your choice. Many feel much safer pulling into a campground. For me, I hate to reserve a campground when I get to that point and I might have the energy to drive another 2 hours, or vice versa, I get too tired before I get to the planned stop. While the cost of the campground for 5 - 8 hours is an issue as well, it's only a small issue. If, however, you are taking a more leisurely trip, then I would recommend stopping at campgrounds and enjoying the sites on the way. (We typically don't have that much extra time).