Really, there is not much of an issue at all with "ironing" rather than "pressing" yardage. Where it becomes more important actually is when ironing seams while piecing. This is when aggressive "ironing" of a seam or a block instead of careful "pressing" can distort pieces or blocks. Also, there is unlikely to be any issue with yardage being "off grain" after ironing. "On grain" cuts are more important in clothing construction rather than quilting. This is because with clothing the pieces tend to be large and the direction of grain affects how the garment drapes on the body. Quilt pieces are, for the most part, small so grain becomes less of an issue. If you starch yardage heavily before cutting, you can even piece bias cut edges with no distortion (assuming you are careful). If you handle cut pieces carefully, blocks carefully, sashings carefully, and the unquilted top carefully, off-grain cuts won't matter. As long as the quilt top lies flat, you can quilt it and, once quilted, grain is no longer an issue at all because the quilting holds all the layers together in harmony.
