I'm not trying to get focus perfect, just shape perfect. If you print a photo and the verticals are messed up or you want to show it uncropped and window mat it, you want it to be a proper rectangle/square, not some skewed rhombus on the paper. Even if your 10x10" print is off by 1/8", it shows bad when put in a mat where you want exactly 1/4" all around.