courtesy Bishop Clothing Construction book
"Directional staystitching is rarely used in couture, and never on necklines as is often recommended nor on armholes. If you are concerned about stretch, fold a bias strip of silk organza over the edge and hand baste. The thread itself will prevent stretch.
As to directional stitching, if a seam is hand basted, as it is assumed to be in couture, you can sew it in any direction and retain control if the seams are of like grain. If they are of mixed grain, follow the weakest grain on top and handbaste, then machine baste. ".........................................Roberta Carr in "Couture, the Fine Art of Sewing" ( bolded words as originally written)
Do you stay stitch? Do you do it directionally?