It sounds like it's just a test to see if your backing is taunt enough. You want it taunt but no so much that the backing is stretched out of shape. The time you take on this process could mean the difference between puckers in your backing when you are quilting or a smooth back to your quilt. I've also heard that if you drop a dime on the backing after you have it taped down & the coin bounces up then it's taunt enough.
