This is one of those things that seems to be mostly a matter of preference... I started out doing what I thought was "following the rules" and pressed to the side but by experimenting with both ways found my work was neater and my joins better when I pressed open. So that is what I do most of the time. Sometimes the configuration of seams tells me otherwise and when they do, I listen. Maybe the seams are not as strong... I haven't had a problem yet. But then I don't quilt for prizes, profit or posterity. I do it for my own pleasure and just hope what I make is pretty enough that someone else will like it. I want it to be used and enjoyed and don't have any expectation that it will still be around 20 years from now.