Proper burger cooking technique: Do you flatten the patty while it's cooking?
If you watch some video of people cooking burgers (over grills or on griddles), you'll often see them flatten the patty with the spatula. Wouldn't this squeeze out all the yummy juices and make the burger thinner, thereby prone to cooking faster and getting dried out? Or does it drain the burger in some special way, and get it to cook more evenly? What's the proper technique?