Both--since it rids ground beef of up to 50% of the fat that is cooked and brought to the surface, both. Do this today, cook up some burger/ground beef and put it into a dish and leave it in the fridge till tommorrow morning. Let me know if you feel like chowing it down after looking at the contents of that dish, because all that white solidified fat you see is what's going into your body if you dont rinse after cooking.
If its too comical for you to do or just a pain in the ass to do after cooking, hey be my guest in chowing that down, might as well pour the liquidfied fat thats in the pan and drink that down as a chaser.