The last quilt I did with homespuns, I regretted not washing. It was lots of greens, the color got all over my hands as I was cutting and sewing. So when I finished I had to wash with lots of color catchers to keep it from ruining the tans. It crinkles when you wash it even after prewashing because of the loose weave.
If you are using strong colors I would zigzag the cut edges and prewash, just to save the headache later.