You can never press too much in my opinion. Pressing and I do mean pressing not ironing keeps your blocks neat and nice, easy to work with and put together. I also use steam in pressing, I don't use a lot of starch since my blocks are neatly pressed and don't need repeated starching to make them stiff. I press each seam as I create my blocks and then every time a piece is added as in sashing or other blocks everything is pressed, even a finale press before quilting.