I think the bias edges are not a problem at all if you starch heavily before cutting, as others have mentioned. It is probably a manageable issue if you use unwashed fabric, as there is typically a lot of sizing in it straight off the bolt, which helps keep the fabric stable. The bias edges could present a real problem for quilters who like to prewash fabric and do not starch it before cutting; the prewashing takes out all of the factory sizing, so there is nothing left in the fabric to prevent bias edges from stretching wildly out of shape as you work with them.