I think it is a matter of strength of seam. we were taught in basic clothing class to always press the seam open. I believe the original theory with quilting was they were all hand done and the hand sewn seams were stronger pressed to side. Now in todays world, I think it could be more a matter of choice at this point. If I was making a childs quilt which I knew would get a lot of wear and use, I would press to the side and sew with a shorter than average stitch. A quilt made for display (wall hanging) or for an older adult I would do what ever worked, especially where bulk was an issue. However if matching seams is going to be important in the overall design of the quilt, I would definitatly press to side and make sure every seam was locked into place, with one seam going one direction and the other seam going opposite direction, that way your seams will ALWAYS match well. and yes on some very bulky seams I have pounded them flat with a hammer !!!!