I was still in the dark. Found this - hope it helps others.
Pressing to Set Seams
An Easy Way to Make Accurate Quilt Blocks
About.com Guide
See More About:pressing basicsquilt block constructionBefore you press a seam allowance to one side, put your iron down on it flat, just as it was sewn. Don't move the iron back and forth--let its weight do the work for you. This step "sets" the seam, flattening puckers that occurred when it was sewn.