Remember that all fabric is treated with formaldehyde. It comes from overseas, and is required by law to be treated to kill any insects. Nasty stuff. I work in an LQS, and by the end of a day of cutting, my hands are sticky from the chemicals on the fabric.
I prewash everything except precuts, but am sure to wash the finished project in that case.
If you zigzag the edges before washing, there will be no ravelling.