I agree that the fabric grain is most important in garment and some home dec projects, like curtains. The sewn item needs to be on grain or it will not hang right. It's a bit less important with a pieced quilt because of all the small pieces. The only way to get the grain is to tear it or pull one or two threads, which is hard with cottons. I tear to get the straight of grain, but as I've read in numerous quilting books, pattern rules all. So if the pattern is printed off grain, and the quilting patches are big enough where the 'off' print will br noticeable, I ignore the grain and cut the pieces aligned with the print.