When we buy wool or thread already rewinding without spool, this allow us, when we begin to work, pull the thread from the center of the ball.
This makes it easier faster weave and without tangle. Keep the ball rolling and brake the thread when we throw the weaving.
Sometimes you cannot find the tip so easily and end up doing the worst knot the world ... but calm, with patience you will find it. It is better to invest time looking for the tip of the center ball, to fight with the ball until it is finished.
Besides weave and without tangle faster, we avoid wool or yarn gets dirty at every turn.