By the time good quality, highly processed fabric reaches the consumer, it is usually shrink-proof. A dense thread count usually indicates high quality, shrink-resistant fabric. Disadvantages of Prewashing Washing fabric before using it requires more time and effort. The unfinished edges of small pieces often ravel and get tangled in the washer and dryer. You'll also need to press the fabrics before using them.
Washing also removes sizing which provides stability.
This stability is beneficial during cutting, piecing and quilting. You can replace the sizing by using spray starch when pressing the fabric. Fabric softener eliminates the stability that makes the fabric easier to handle, so using it is not recommended. If you use mild soap, cool water and a gentle cycle of hand wash and air dry your quilt flat, then it is not necessary to prewash. If you are making a wall quilt that will never be laundered, then prewashing in not necessary.