Pounding a Chicken breast out to make it more uniform for cooking. If you want to grill it like a hamburger well okay pound it flat. The uniformity at witch it cooks depends on it on a dry grill that going to dry it out even more. Chicken breast should always be cooked in a pan. With plenty of Butter, or Chicken Broth, or even just water with seasoning on it. Chicken Breasts cooked at 300 F on the grill for 3 minutes on both sides then put in a pan are the best ones. Put tin foil on the pan and butter away. If you put it in a pan and take it out more than 10 minutes before you eat it. It will still dry out. Leave it in the pan to your immediately are ready to eat.
Chicken Breast aren’t used in competition because they dry out fast.