I've washed them - but I also use the "hand wash" cycle which is a very slow agitation.
I only do this if there are "issues" and I figure it needs it. Since I inherited a bunch of my Mom's UFO's - and some have rodent stains - I want to make sure they will clean up before putting the effort into quilting them.
But then I also prewash ALL my fabric purchases - which has included about 7 bags of scraps and small yardages. They smelled smoky - and if I'd not got that out, I wouldn't have used them (BTW - I bought one bag and washed it, and when it "worked" I went back and bought the rest). Also went through a gallon of vinegar.
I did trim off all the loose threads between the washer and dryer. And I would get a quite a handful with each load.