Sometimes I set the seam and sometimes I don't. Just depends on how much I care about the finished quilt top. I do find that I don't have those little puckers when I do the first seam set and then press the right way. I use a 50 wt cotton thread to piece and don't really see much seam loss. I almost always sew a scant 1/4 inch seam anyway, unless the block is one that has all the same block pieces each way....4 patch, 9 patch or 16 patch and that is all that will be in the quilt. In this case it doesn't matter. All blocks will be the same size. If you are mixing these blocks with others that have multiple seams then the blocks have to match. That's when I really look at finished sizes.