never heard of cutting scant 1/4" but do use for seam allowance. the idea is your seam is about 2 threads smaller than a 1/4" seam allowance which allows for the thread's bulk when you press the seam. I learned to cut my fabric so that the ruler marking is set so the fabric edge is barely on the "outside" of the ruler marking, which lets you cut just a couple of threads wider than the measurement--always better to trim a too big block unit than to have a too small one!
too check the width of your seam allowance, one thing I learned on this Board, was to cut two perfect 2.5" squares, sew together with your 1/4" seam allowance (or scant 1/4") and press open well and measure--it should be a 4.5 " rectangle