Why roll yarn into a ball?

I find it is easier to use as it comes from the store both for using it and storing it. The only time I have to wind it into balls is when I make a mistake, then pull it out and have a lot of yarn laying around and then the winding starts.

You can buy yarn 2 different ways. If you are buying an inexpensive acrylic yarn such as Red Heart it comes in a "Pull Skein" that is ready to use. There are instructions on the label on which end to pull from the center.

Most wool is purchased in "hanks". The yarn is not wound up, put is loose. This is the type of yarn that must be wound in a ball before you use it. When you buy this type of yarn you are buying it from a yarn store or on-line; not from a box store such as Wal Mart or a craft store. If you buy it from a Local Yarn Store they will wind it in a roll for you. Usually the first 2 or 3 balls are wound for free, any more than that for a small fee.

You don't. It's a modern affectation. They never did that before. It's more convenient for people moving around, but is not necessary. There is a right and a wrong way to make a ball, as there is a right and a wrong end from which to pull the end, so be very careful on that point. It's just as easy to use the yarn from the skein (the large circle of yarn, or a hank) as it is from a ball.

Keeping the yarn in hanks helps to keep it tangle and knot free (if stored properly). However, its much easier to knit from a ball of yarn instead of a hank, particularly if you are machine knitting.

winding up yarn into a ball helps because it takes up alot less space than a roll and they doo sell it in a ball at lots of places like wall-mart