I wash. Every now and then I still get a fabric that bleeds like crazy -- usually batiks but occasionally a regular print -- and every now and then I still get one that shrinks more than others. I think it's also easier to see after washing and machine drying whether the print really is printed on the straight grain of the fabric.
I've never used charm packs or jelly rolls because I can't figure out how I'd get them washed and dried without taking lots of trouble LOL .