Sometimes you have to go full speed, changing directions and jumping hard, in order to split the defense. But the hoop comes at you fast when you're dribbling all out, making a soft finish nearly impossible. The finger roll allows you to attack the hoop at full speed while finishing soft, increasing your chances for a bucket.
Dribble straight at the hoop; there's no need to angle yourself to the backboard like a layup. Pick up your dribble with both hands at the waist while running and jump off your lead foot. Lead with your left foot if you intend to shoot right-handed and your right foot if you want to shoot left handed. As your body drifts towards the hoop, use the momentum generated by your legs to cup the ball in the palm of your shooting hand and raise the ball to the hoop. Release with a flip of the fingers at the top of your jump. Reach as close as you can to the lip of the rim for a soft shot, even at full speed.