Most of the time I do press my seams to one side..but I have also had times when it will work better to press seams open and it works well...and yes, it does reduce the bulk and help with FMQ. I think the pressing to one side is helpful when you want to "butt" seams together.
Do wonder why you sew your strips twice? Doesn't that add more bulk to the seam? Wouldn't that be harder to press open?