The Haynes manual mentions that before checking the timing, I need to short 2 pins on a service socket located under the dash on the passenger side. I wonder if this is really necessary and why? I checked with my timing light without doing this, with spark plug wire # 1 clamped to my timing light and the timing seems to be correctly set up as I could see it aligned with the red line on the crank pulley.

What exactly will this 'shorting pins' procedure do?

Thanks for any inputs....