I tried setting the seams and found it actually made my block not lie as flat. When you set the seam, you're pressing one side of it 180 degrees from the direction you want it to eventually go in. So the top piece in the sewn pair, having been ironed in the wrong direction, now has to flip and iron down crisply the other way. I found this created more of a problem than it solved. I quickly went back to simply ironing the whole seam in one direction and leaving it at that.