As I understand it, I think you're talking in regard to the AT through the Smokies. If so, then you are required to have a reservation and stay in a shelter unless you are a thru hiker. The park defines a thru hiker as someone who started the trail 50 miles before entering the park and will continue on for 50 miles after leaving the park. If you are a thru hiker, you have to stay in a shelter if space is available, but this can be avoided by dawdling around and allowing others to take the shelter space ahead of you.
"If you play a Nicleback song backwards, you'll hear messages from the devil. Even worse, if you play it forward, you'll hear Nickleback." - Dave Grohl