A scant 1/4 inch seam is just a shade smaller than an actual 1/4 inch, by just a few fabric threads. It's recommended for all block construction because by the time you press a seam to one side it's a shade larger than the seam you actually sewed. Does that make sense? Marcia explains it well at her
web page . Scroll down to the bottom of the page. I personally never use a "scant" seam because I almost always paper piece. For that you just follow the line. When I'm not paper piecing, it still doesn't matter to me if my blocks come out precisely the same as the pattern, as long they come out precisely the same as each other. This is something I'm still working on! So I always use the same guide for my seams, scant or not.
