As a rule, I've always pressed to the side because that's how I've been taught. But, now I'm considering pressing them open to avoid what Lori S described as a "pile up". Have had that happen more often than I'd like. It is true that it is the stitching that holds pieces together, so to compensate and make myself feel better about pressing them open I'm considering shortening my stitch length to add more stitches per inch, ultimately adding strength to the seam.