I have always wondered why people put oil or butter in a pan before browning ground beef. It doesn't make sense since you end up having to drain the grease in the end anyways. What is the purpose of the oil or butter? Is it used for pans that are not non-stick? Flavor?
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.
Another reason people put butter in the pan because the milk solids in the butter (which separate when the butter melts) contribute positively to the "browning" of meat. So, if you're looking to get a nice brown color on a steak, butter in the pan will help.
If the ground beef is very lean then adding a small amount of cooking oil to the pan is necessary. Otherwise, ultra-lean ground beef will burn and stick to the pan before the center of your burger is even done. Additionally the burger would be extremely dry and unappetizing when cooked.
After it is done squeeze out excessive grease with napkins or paper towels before consuming.
If you add butter to ground beef, say, burgers in a pan, it makes them taste better, and gives them a slight crunch on the outside, and yes, attributes to a better color. Same with steaks. It's not done out of necessity, it's done out of deliciousness.
Saturated fats and unsaturated fats will form a bond producing triglycerides. Rinsing the beef with hot water, practically makes your 73/27 beef into a 90+/10- beef. It's healthier and much more cheaper per pound! With that said, butter may make it Brown and taste better, due to the dairy components and thus adding more saturated fats.