The old familiar half square triangle is common in many traditional and modern quilt patterns. But they are a pain to piece the old school way: Cut out many right triangles, match them along the hypotenuse, sew the bias seam, swear when the bias seam ripples, rip seam out, trim to make the square square, repeat. Pain in the neck!
Someone figured out you can save a lot of time by placing 2 squares together, mark a diagonal line, stitch on either side of the center line, cut them apart and voila! 2 half square triangles without having to sew a loose bias seam.
But there’s an even more productive way to mass produce them eight at a time.