I do prewash and starch. I started quilting without doing either and have had fabric bleed or behave badly after washing the finished quilt. If it is going to present problems I want to know about it before investing my time and energy. Also, when you iron/starch before cutting it requires hands and eyes on the fabric and you can catch any issues such as small holes or flaws that you need to eliminate in cutting out your pieces. Ann in TN