I usually press to the side as seams pressed open can stretch during the quilting and I can see the stitches. You also cannot stitch in the ditch an open seams because you are stitching down the stitches and can break them. I press open the last seam when connecting 2 halves of an 8 point star or similar to reduce bulk in the center. I also press open if I am doing a recut block such as Disappearing Hourglass because the block has to be very accurate to resew back together.