It’s a good rule. I once had a job working for my pastor’s son who ran a business. One time I had a closed-door meeting with him in his office. As I opened the door to leave, a woman who had a business appointment with him was waiting to come in. She stepped in just as I was stepping out. I grabbed the doorknob to close the door when he said, “Please leave that open.” When I later asked him why he did that, he told me about Graham.
That’s a good idea for reputation’s sake. No room for wagging of tongues. He might have been perfectly ok with the lady. If something private had to be discussed there would need to be a way.