For someone in your line of work that rings especially true. If you are #2 through a door and have to engage a threat, freezing in the door to do so will cause a major traffic jam and leave #1 hanging in the wind. Drawing on a drawn gun is another thing to consider. Action is faster than reaction, and if someone already has the drop on you then moving out of the way is probably a pretty smart thing to do, but if you are close enough to them to where you can get shots off with 100% accountability, then why not shoot while you're at it?