Prewashing, for me anyway, is to eliminate shrinkage issues as well as get rid of the unnecessary chemicals (specially for baby quilts). I have more problems with bleeding in solid fabrics, but occasionally will have a bleeder in prints, primarily reds, so I treat with retayne in the wash. Then all my fabrics are ready to go to the cutting table. If the fabric is flimsy after washing, I press with a bit of starch. Making quilts with poly batting and prewashed fabrics will not shrink near as much as with a cotton batt, so not near as much "crinkling". I prefer that over worrying about seams pulling loose because of shrinking fabrics. But as the other posters have said, this is all a matter of opinion. I always wash a finished quilt as it gives me a chance to check for loose threads or seams that have come loose as well as getting rid of any dirt or oils from my hands during construction.