Sashing can correct a lot of errors. One LQS owner showed me how to sew sashing on the right side of a block, then on the bottom of the block then square it up. Do this instead of sewing sashing all the way across a row. This came in handy one time when I was asked to put blocks together that each block was sewn by a different quilter. It was a shock to see what a difference there was in seam allowances. The blocks were suppose to be 12 1/2" unfinished. Well, very few were. The blocks were anywhere from 11 1/4" to 15" (?). I had to trim down on several of them before putting sashing on like the 15" block.
I just did a tumbler quilt where I used a 3/8" seam allowance so that when I quilt 1/4" from seam, I will catch the seam allowance in it. Had no trouble putting the blocks together since they were not intricate piecing and all that mattered was consistency.