Eleanor Burns is the one I've seen do it, especially on a pinwheel block. It really does help the center lay flatter. You do have to loosen the threads down to the intersecting seam or it won't work though. It will make a little pinwheel on the back where you mush it flat, then all the seams will press in a spiral to the left (at least that's the direction mine seem to go). On a 4-patch it forms a little 4-patch on the back.