I don't pre-wash but I always wash the finished quilt with a color catcher. I know someday I will probably regret it but so far, so good.
And yes, that advice about ALWAYS covering the rotary blade is good. I do, but once I left it uncovered as I moved fabric for a second cut (rotary cutter was still in my hand) and I nicked the side of my hand with it. It drew blood even though I barely touched myself with it. You just can't be too careful with those things.