If you make the whole quilt with the same machine, your seam allowances for the whole quilt will be more or less equal so your blocks should fit together. Your 12 inch blocks may measure 11 7/8 instead of 12, but they'll all be that tiny bit small and your whole quilt will be a little bit smaller. So if it's a quilt for you, it's not as critical. If you're swapping pieced blocks w/ another person, it becomes very, very important to have the proper seam allowances.