I don't mind the washing part of pre-washing, it's the ironing and starching part I can't stand. I have pre-washed fabric for one quilt only and that was done because I wanted a smoother finish after washing the finished quilt. Did not like working with the washed fabric at all but the end result looked exactly the way I wanted it to!
I have made a couple of Kaffe Fasset quilts with his vibrant fabrics mixed with white and have not had any issues with bleeding from my unwashed fabrics.