Increased food safety as less likely to leave raw chicken after cooking.
Increased moisture held in the chicken breast.
Lay the breast flat on a clean chopping board.
Place your hand on the chicken breast, apply a small amount of pressure and cut horizontally through the breast from one side to the other, stopping half an inch before the other end.
Open it out and you’ll have a breast of half the thickness. Slice the breast and continue cooking as normal.
Extra optional step:
To make the meat even flatter and more even, with the chicken laying flat, put a sheet of baking paper both sides (above and below the meat), then bash with a rolling pin. The paper stops cross contamination.