I trim all of the cut edges using a rotary cutter with a pinking blade before I wash.
definitely do this! i used to HATE prewashing because of all of the strings that needed cut off. i just prewashed many yards of fabric for a new quilt project after pinking the edges and i didn't have to trim any, not even one, string off! now i don't hate to prewash!
much easier if you invest in the rotary blade versus scissors (if you use the olfa rotary, you can just switch them out. watch for the 50% off rotary sales at jo-anns, if you have one. you can buy the individual pinking rotary blade). really quick and much easier on your hand/wrist!
a light bulb lit up the other day i was at the quilt shop looking at the charm square bundles. they are pinked! guess that's why, so they can be prewashed and won't fray!