When we moved in we found several door stops laying around. Figuring they weren't important we stashed them away. But that first summer we had to dig them back out since several doors would slam shut in a breeze. One of the weirdest though is the kitchen door.
Under the kitchen runs a fresh air duct for the furnace. It was made by tacking metal to the bottom of two joists. The result is that in winter, there is a very cold strip of flooring running through the kitchen. As when most things are cold, the joists contract and the kitchen door swings freely. But come summer, when things warm up, the floor joists expand just a bit. The result is a slight drag on the kitchen door.
Now some people may worry about the kitchen door rubbing across the floor and might even shave a bit off the door. I like to think the builders knew what they were doing by installing an automatic door stop.