I always wash after completion. There can be any number of things that need attention that you simply won't see until it is washed. I also want to eliminate any dirt, markings, oils from my hands and cat hair ( they are quite persistent in trying to gain entrance to my sewing room). Your quilt will look different after washing, but not necessarily in a bad way. How much different depends on a few defferent things.....the type of batting used (poly does not shrink), were the fabrics prewashed (prewashing helps eliminate fabric bleeds as well as shrinkage), cotton thread versus poly, etc. You also don't want the recipient to feel like they have ruined a quilt when it comes out of the dryer all crinkled (is what happens when you use cotton batting...very desirable to lots of us quilters).