I try not to sew over pins, but sometimes I need the pin to hold "whatever" in an exact place. I slow way down when I am going over a pin. If you break a pin or a needle, it can leave a hole in your seam, ask me how I know. I have sewing machines that are expensive and some antique ones, including a FW. None of them like to go over pins. As far as not pinning in the seam line, you risk the chance of not getting your seam edges straight. If you are not pinning in the seam line there really is no point in pinning the seam. Just my thoughts and this is the way I teach.