I am taking Leah Day's FMQ a Sampler class on Craftsy. She advises to press the seams open, even for stitching in the ditch. She says she's never had a problem with a seam coming open or shredding the thread. I've always pressed to one side, but my current project I'm pressing the seams open, and I'm going to SITD. It will be interesting to see what happens!