The method the OP did sounds like sewing a square to either side of a rectangle. Yes you have to trim away the excess triangles in the corners but I have found the resulting triangles that are trimmed away can be sewn together to form HST. If your finished FG measures 2" x 4" your "scrap" hst will be 1 1/2" after trimming. I have loads of patterns that use that size and am saving them up to make a scrappy quilt in one of those patterns. It is only a waste if you toss the triangles bits you cut away. But if you save them in a ziploc baggie and sew them together ala Bonnie Hunters "leaders and enders" method they will accumulate quickly. And you will have them in perfect colors for more QOV quilts.