1) When you are on a trip away from home, you may not want to bring your swift and winder.
2) When you are riding in a car/plane/train/boat, and you don't have a time or space to set up your equipment, you can drape a skein around your knees and wind a ball by hand.
3) You can stop midway and finish winding it up later, because it's portable and you don't have to take equipment apart and put it away.
4) Your center-pull ball will be as soft as you'd like. I often wind with one finger under the yarn wraps, as you'll see in the video. But you can put no fingers or more fingers under the yarn wraps to make the ball harder or softer.
5) While winding this way, you will find every knot or nub or imperfection in your skein, before you ever start knitting with it. Better to find out now, rather than in the middle of a long row, that you have a big knot in your yarn.
6) Children who are learning to knit often enjoy making this special center-pull ball that never tangles.
7) You can do it anywhere because you're a super knitter!