I have always pre-washed any fabric I was sewing. I startred sewing garments many years ago, and I always felt it if it was something that was going to be washed and dried after construction, why take a chance of shrinkage. Also, if fabric has been pulled "wonky" on the bolt , then washing and drying will show that it is not on the straight. I then know to pull from the edges and bias to get it as straight as I can, then pressing. It does take a little prep time, but sure saves heartache later. And cottons, linen and wools are always going to shrink!