Been quilting fo 10 years and my teachers, Alex Anderson's TV show and her guests, always pressed to the dark. Recently quilters seem to be favoring "pressing open" to reduce bulk, especially at joining points. I keep saying I'm going to start pressing open, but I keep forgetting to do so:>)
Pressing to the dark added more stability to the seam, less likely that threads would break and open the seams. Now with adjustable seam lengths and a variety of thread strengths - not so much of a problem.