I press to the sides 99% of the time. There are certain blocks that have to have the seams open to lay flat. When I press the seams open I can see the thread and I don' like that look. If you press the seams to opposits sides you have two layers when you join the blocks you have two layers on each side of a joined block. When you press the seams open and join to another block you still have two layers. Again as several have said, Do what works best for you. We'll keep the quilt police away from your quilts. :lol: