Or any reason a broker cannot execute a trade for you.
One should always set up three trading account being able to trade electronically and through the trading pits. Being able to get the floor tick number the ticket from the pit not the ticket number from the floor clerk because this pit ticket is the only that can be used to exit the position later. Your broker has that ticket number. I never traded without getting it as that was one of the requirements doing business with a broker.
When your broker is having trouble say with phone down and you can not get your order in, you know that broker that has been bugging you for your business well you can call him and ask him to do a curtsey trade and get you out of the trade as he can with the floor (pit ticket number) can execute that order and close out that trade for you. That is how important the floor (pit) ticket number is to have. I had to do this one time because my brokers phones went down and had no contact with them.
If you are trading from a electronic platform, I am not sure how you would go about the right ticket number ? But would be asking my broker questions about it that's for sure. I believe for the most part I would be trading directly to the floor and only use the electronically trading order platform sporadically based on other reasons.