Tactical flexibility may reduce the chance of you becoming a target.
In a gunfight you must make yourself as compact as possible, to get behind cover and concealment. Otherwise you can potentially expose a leg or an arm or another part of your body.
When it’s time to return fire and go on the offensive, you need the range of motion to place your body in the optimal position to get the shot. Being tactically flexible gives you another opportunity to win.
You may be a law enforcement officer sitting in a patrol car. You start out in a resting state. In an instant you get a call and must leap out of your vehicle.
Are you physically able to jump out quickly and go into a full sprint?
Perhaps the suspect leads you over a chain-link fence.
Can you raise your leg high enough to get that first bite on the chain-link fence?
Can you quickly grab the top of the fence and pull yourself over, while wearing 40 pounds of duty gear?
And now it's time to fight.