I wash prior to cutting due to skin allergies to all the chemicals in the fabric. Also it gives the fabric a chance to shrink if it is going to so I know that I have enough to finish my project. Plus the bleeding factor. You can not always tell which fabric will bleed. LQS or chain store, all have bled at some point.
Pre washing is a personal preference but I would rather "waste" my laundry soap, water and time then ruin my project! I always iron and press with Best Press after the fabric is washed so I regain the stiffness that makes the fabric so nice to cut.
I don't, however, wash charm packs or jelly rolls. I do pay the price as they make my skin itch, itch, itch!!!