I only pre-wash things that will likely fade and run, like Reds. Other wise I piece the quilt and when it's finished I give it a soak, not an agitation, and then dry it to remove most of the dies, finishes and get some shrinkage on it. Once quilted and binded I wash again with agitation and dry in the dryer to make sure it's completely clean and nice and fluffy. I might do things differently if were a heirloom quilt, but one that is to be used by family and babies etc. get the washing treatment.