Everyone has an opinion on this - kind of like a religion question. I think most people pick their wash or not wash based on their personal experience...or someone told them once they MUST do one or the other.
Personally, I ALWAYS wash. Maybe it is the hand dyer in me. It is also the problems that I have had (2 bad ones before I learned) of bleeding fabric (high quality $10.00 yard) on my needle turn applique. All that hard work wasted. I also had an issue in the past where I stitched and then washed. One fabric really shrank compared to the rest and wherever that fabric was in the quilt, there were small puckers as the seams of that fabric pulled against all the others.
Whatever you decide, I wouldn't wish my bleeding problem on anyone!