Of all the skills that are fundamental for fighting – move, communicate, shoot as necessary, use cover and think, the communication is one of the most difficult. We communicate with people every day, but under stress the ability to communicate is something that won’t happen if it’s not part of our standard response.
You communicate with the threat, issuing verbal commands, telling them what you want them to do. According to the documentation, the presence of a firearm and strong verbal commands will diffuse the situation. When the threat(s) don’t comply then we gain compliance with accurate fire. Now, there are some situations where you wouldn’t issue verbal commands in order to maintain the element of surprise, but if you don’t make communication part of your practice you definitely won’t remember to do it.