I think I have another reason for not pre-washing your fabric (unless there's a possibility of the colors running, in which case you definitely should).
One advantage of the old, wrinkled look is that it hides the imperfections in your FMQing. I just took a break from FMQing a queen size quilt (wow, is that big and hard to manage) and I really suck at it. My curves are so wavy (where not intended to be so). I am definitely counting on that not being so obvious after washing LOL.