I usually do not wash new fabric before I put it away. However, when I am ready to use it I use steam to press it before I cut it. I do know that the steam can cause some shrinkage. I also know that if fabric is going to shrink it will shrink the first time it is exposed to water or steam. I would rather have that happen before I cut the pieces. Some people think that the shrinkage won't happen if they cut, don't use steam when pressing and finish quilting it. The fabric will still shrink when you wash it in the finished product. I believe that shrinkage at that point stresses the seams or the fabric around the quilting design which will cause undo wear at those points. So, I press early and often so the patch, square, row or border will be relaxed during construction and not cause problems later.