I always press and starch. I cannot cut or measure any fabric without all the wrinkles being removed first. I cannot sew the next seam if there is a wrinkle. Call me anal, but I don't like the movement of wrinkles that can cause seams to be even remotely wonky. Starch is one of your best friends when doing OBW, second only to using those straight pins. I also press the seams open, because the OBW I make are wall hangings, not quilts that will be used and washed.