I've had this option set to off since csx hh, and never noticed it does anything. However, today I derailed a train by going over a switch that was not set correctly, and was shocked to say the least. Tees valley route, class 37 service 0Z07 7:40. Once the coal is loaded, you are prompted to go forward over the 2 switches I marked red in the screenshot. And if either of these switches is not set correctly, while having the option from the title set to off - boom, you will derail. Funny thing is these are the only switches in the game, that I know of, that can derail a train this way.