it depends on lots of things...if it's batik's, hand dyes, or any i think may bleed, i pre-wash; if it's flannel, homespuns, or a loose weave fabric, i pre-wash. if i absolutely do not want something to shrink, i pre-wash.
if the fabrics are good- high quality, quilt shop fabrics and i am making a bed quilt i usually do not pre-wash; i wash the completed quilt after binding. which i always do, no matter what, even if the fabrics have been pre=washed i still wash the finished product.