I recently quilted a beautiful quilt in burgundy shades for a customer. She had pressed all her seams open which wasn't a problem since I wasn't doing any SID. But she pieced it with either an off white or a light gray thread. To my horror, the nature of the longarm putting pressure on the seams caused that light colored thread to show in several seam lines. Made a stunning quilt look not so stunning up close. So, if you press your seams open, it's best to match your thread color to your fabrics.