Pressing seams to the side results in a stronger seam than pressing them open. There are no quilt police. If you want to press them open, go for it. There are several nationally known quilters who do so. However, I will tell you that the seams near the top of the quilt, which get the most use, are also the ones more likely to show threads, so make sure you match the threads with the fabric rather than using a generic color, at least for that top row.