It's not a matter of being perfect. It is a matter of ending up with the block size that it is intended to finish up at. If your block is to finish at 12.5" and you don't use the scant 1/4", your block will finish up smaller. The scant is for allowance when pressing the seams open, not because designers are trying to make your quilting life harder. Just move the needle over 1 or 2 notches to the right and you will be fine and won't have to worry if you have a true 1/4" or a scant 1/4".