to me the purpose is to make the final result fit the size needed. ie the goal is to have a 2.5 square finish to 2 inches square when pieced into the block. I know where to position my needle to get this result when I sew however if I happen to be sewing with a different thread thickness I might have to adjust my seam a bit etc. I don't care whether it is actually scant or by how much as long as it holds together and produces the final result.