A pre-drawn handgun reduces the "get stabbed before I can react" range dramatically. The general rule of thumb is you need a knife threat to start at least 21 feet away to draw, aim and fire(See - Tueller Drill). When already at the low-ready that range drops down to ~10-14 feet, if I recall.

So if you might need to defend yourself, but you want to avoid escalating the situation by aiming a gun at someone, it makes sense.