As I understand it originally quilters pressed to one side because the batting they were using tended to leak out between the stitching if the seams were pressed open. By pressing to one side there are no holes for the batting to leak (beard) out. The batting that is used by today's quilters does not beard as much so it is not as important to close up the holes by pressing to one side. I do feel however you get stronger seams by pressing to one side because ther is no pull against the seam like there is by pressing open so that is how I press. Different techniques are used in quilting than are in garment sewing or tailoring.