It depends on how intricate the block is and whether the seam would cause a natural bump if left as is. If there would be a problem with bulk in the center of say a intricate pinwheel type block, I press them open. Some blocks cause a problem because they would bulge naturally after the finished block is done. We don't want a tent now do we? LOL... Yes double battings help but, why not do the extra step?
Also consider the fabrics you are using. If you are using a tight woven fabric, such as batiks, getting a needle though all that bulk to quilt it will be very tough and can break needles while machine quilting it. Which by the way can throw the timing off on your sewing machine. Or heaven forbid having to hand quilt though all that. So yes an open pressing is best for intricate designs or bulky materials.
Last edited by RedGarnet222; 10-25-2013 at 08:36 AM.