I have been been pressing open for almost fourty years. Never had a quilt with seams that broke or batting that poked through. Most newer battings have a scrim that keeps the batting from migrating.
It is a preference , I like a flat block, and it makes it easy when it comes to joining blocks ...as I never have two joining with the same direction,at the same point, making for a really big bulk at the join.
There have been a few occasions that I have pressed to the dark , only because it is a bit faster.