Steaks start out virtually perfect, especially when you get a good steak. One rule about the way steaks cook is that the fat is going to shrink faster than the meat. This can cause the fat to fold or compress the meat. This pressure can squeeze out the juices and make the steak more difficult to eat. So sometimes you need to trim a steak to make it cook better. You will also reduce the risk of flare-ups by reducing the amount of fat. Of course the fat is important to the flavor of a steaks so you don't want to cut it all off.
Here we have a nice New York Strip. This steak has a nice thick strip of fat running down one side. This strip of fat is too thick to really benefit the steak. Of course you could leave it all there, but you will do your grill and your heart good to trim it down. You also need to consider that this strip of fat is going to shrink a lot more than the meat so you need to break it up a bit.