I ever prewash and with higher quality fab I never seem to have any problem. If Fons and Porter don't do it why should I.

My batiks have never given me any trouble when I wash them.

I dye most of my own fabric now and yes please do wash it. I don't care how much they are washed, some dyes just want to bleed.. It's heartbreaking to have a finished project ruined by bleeding fabric.