I have never bought a precut less than a fat quarter and I prewash those along with everything else. I did get a free charm pack (5" squares) from Missouri Star, it was one of the daily deals. I really liked the fabrics in the package but haven't thought about using them yet. I don't know if prewashing reduces lint or not.
When I made my all flannel double sided quilt (out of all prewashed flannels) I had a lot of lint in my bobbin. It also created a good amount of lint in the bobbin area of my longarm. I also notice the extra lint in my LA bobbin on any flannel backed quilt. I know it isn't the thread because I am using a trilobal poly that makes no lint. So prewashing doesn't help when it comes to flannel.