the knee lift, allows you to keep both hands free, for sewing, etc....the stop/ start button, is even better, I use both, and can't begin to tell you how glad I am, that I took the time to learn the stop/ start button. I practiced with some scraps, to learn it, and the speeds. I used a slower speed to learn, then as you are comfortable, increase the speed...it really doesn't take long to learn this, and is so well worth it!