I never wind my yarn into a ball, unless it's in a hank.
And I've seen some knitters ruin their yarn by winding it into a VERY TIGHT ball. This stretches the yarn, and messes it up.
When you knit with tightly-balled yarn, the yarn might relax and your gauge will change as the item sits. OR, even worse, the yarn will be stretched out of shape forever and look too thin, making your item look strange.
A few times, I have received tightly wound balls from well-meaning friends. I always graciously say thank you, then immediately take it home and re-wind it very loosely on my ball winder. I kinda feel sorry for the yarn when it gets stretched out like that. :teehee: