Scoring duck breast helps render all the duck fat, making the skin ultra-crispy!  If you score the duck, use a sharp knife and score the skin lightly. I recommend doing this when the duck breast is cold out of the fridge so it’s easier to slice. I prefer scoring the duck so that all the fat is rendered, but it will not affect the quality much if you choose not to. *I also think it's easier to score duck after having cooked duck breast once before. :)