In nasty weather (snow storm or thunderstorm), even people who usually prefer to tent/ tarp will squeeze into the shelter. The shelters in the Smokies are rated for 12 people, but in a pinch they can hold 20. I've been one of 19 people in one of them - and there was room for one more. Nobody complained. Nobody asked people to set up their tents outside. We just made room. It didn't even suck.

That said, it is not uncommon that people will wait around until after they eat and relax for a bit, hoping the shelter will fill up so they can set up their tents. Lots of people simply prefer not to stay in shelters.