I am in the habit of pressing seams to one side, but when I made the quilt you see as my avatar, I wish I hadn't. most of the sections were either HST's or flying geese. I was chain piecing and pressing, so everything was pressed the same way. When it came to assembling sections (some were turned in different directions), I discovered that I should have pressed some to the opposite side, but I didn't go back and do it again. I grew more and more frustrated with the amount of hard pressing I had to do to keep the blocks nice and flat. (I also warned the longarmer about the bulky intersections. She assured me that she used strong needles, and didn't end up having any problems, thank goodness.)
That lesson learned, I will be pressing at least some of the seams open in my current and future projects. The current project is a hopscotch pattern. Some of the blocks are pinwheels (made of HST's) and the others are 16-patches. I'm definitely going to press the 16-patch seams open so that there are the same number of layers everywhere. I have already pressed the HST seams to one side (habit!); it remains to be seen how well they "nest". If I'm not happy, I'll be doing a lot of re-pressing!