A crumb quilt uses your smallest pieces. The smallest I have used are probably 3/4" unfinished. How big you would use would be a bit subjective. My biggest might be 4" by 3" or 6" by 1" finished. Have you even seen a Victorian Crazy Quilt? Every shape imaginable but not too much in the way of curves. Scrappy but slightly controlled in mine. I cut mine to 6 1/2" square unfinished blocks then used 1 1/2" sashing in one colour which of course gave it more cohesion. Fun.