Specifically, Billy Graham (and his associates) had a strict policy: Nobody was allowed to be in a room with a woman alone - another person always had to be there. This applied to secretaries and other assistants. They assumed that all men would be subjected to extraordinary temptation.
My church, a small one, has lost at least one pastor in the past because this rule was ignored.
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.
And even if there wasn’t such a temptation, people could misunderstand and enemies mischaracterize what was innocent.