I have stayed at WM several times when I drive late. Have also stayed at Cracker Barrel several times. Never had any problems, just pull in and go to sleep, get up the next morning and do our shopping at WM or eat breakfast at Cracker Barrel. Have also stayed at truck stops a few times but they are way to noisy for me. We only do this when we drive past 10pm at night. The only reason we do is so we don't bother the campers in an RV park. It is not to save the cost of the park. I don't think anyone would like my rattling diesel pulling in beside them at midnight.
Some people get all upset when this comes up. Don't pay any attention to them. Do what works for you.