I like to press my seams to the side. Pressing them so that they nest when putting two or more sections together. I feel that if you press the seams open, your quilt looses strength, as all that is between the sections is thread, which over time weakens and the sections can split apart as the thread weakens, becomes loose or breaks, either through age, repeated washings/dryings, and/or repeated tugging/pulling of the fabric with use.