What I read somewhere was not to use the sheets because they have a higher thread count which means it has a tighter weave. Supposedly this makes the needle pierce the fabric, which leaves holes, instead of separating the fibers. If this is true, you should be able to use a needle for knit fabrics to solve this problem. My grandmother was a quilter and always used sheets. I realize in their day and age they were thrifty, but it worked just fine. So I guess it's just a matter personal preference. I'm sure it's the quilt shops that say you cannot use sheets, because they want you to buy their fabric.