It just depends on the pattern that you are working on. I normally will press to one side. One of the biggest reasons for doing that from what I have heard before is that with open seams you may get bearding from the batting coming through. Also when doing SID you want to do that on the low side close to the seam and you don't have a low side with seams pressed open. Right now I am working on Eleanor Burns day and night pattern and you use both pressed to the side and open. The reason for pressing open some of the seams is so that when you put the whole star block together it helps for get the middle where all the seams meet up to lay flat and form a pinwheel like center for the seams.