Crock pot questions?

I just bought a new crock pot and I love it… but between my search for recipes and my love of watching the Food Network, I’ve gotten some conflicting information.

Do you always have to have some sort of liquid in the pot? Say, pot roast with veggies or corned beef and cabbage… can you just throw the hunk of meat in there and let the juices/condensation be the liquid? And something like pork chops or chicken, can they overcook and dry out if they’re sitting in liquid (soup or broth?)