Why do people put oil/butter in pan when frying ground beef?
Transfer of heat. First you need a hot pan (sprinkle some drops of water on the pan, it should sizzle). Then you add a drop of oil and swirl it around. When the oil forms a striated pattern, it's hot. Then you put the meat in.

The hot oil helps to transfer heat from the bottom of the pan to the meat. You only need a spoonful of oil.