I'm thinking you mean a stretch needle, one that you would normally use for knits. This needle has a deeper "scarf," an indentation that allows a longer thread loop to form, making it easier for the bobbin hook to grab it, so you don't get skipped stitches. In some cases, a ball point needle is also referred to as a stretch needle. The ball point needle will slip between the threads of a knit (stretchy fabric), not cut them and allow the fabric to run. Since you are sewing on cotton fabric, I'm not sure that I know why it would be an advantage.