A lot of the rules quilters lived by went the way of the dinosaur, just like scissor cutting your fabric.
Most fabrics today are of a better quality than of days past and shrinkage is minimal AND predictable.
That's why I don't prewash, and I've never had a problem.
But I do like the softer look of a quilt that has been washed after quilting, so I wash them before I start using them.