I always iron before cutting. I am working on a quilt now that has 22 different fabrics in all the blocks Except for the background, I didn't have much to iron as it was two small pieces. If it is 1-2 yards I usually iron the whole piece. If it is a large piece, I iron some beyond what I need. Usually I iron one piece of fabric at a time, cut what I need, then get the next fabric.