Bigsister63 is right, grain isn't as important for quilting as for clothing. But, I still like the fabric to be pretty square. I'm afraid that the blocks will get wrinkled looking if things aren't at least a little square. Washing the fabric will remove a lot of the sizing (starch) that is put on the fabric in the manufactureing process. When they fold and wrap the fabric it can get twisted. And, you can stretch (corner to corner) to help as well. The salvage edge is the true lengthwise line but the crosswise is the grain that gets off square.