Alot of yarn comes in a hank, which is fine, but hard to knit from. It is great if you can have your working yarn in center pull ball.
It is possible to wind a hank into a center pull ball by hand, but it takes around 40 mins. If you use a ball winder, then that cuts the time down to around 20 mins, since you have to unwind the hank and then wind it into a ball. The yarn swift makes it possible to do this job in 5 mins!