While I’m not a big fan of the whole OODA Loop concept for casual shooters, it does provide an adequate example of the benefit of speed in a self defense encounter. The four letters in OODA stand for “Observe, Orient, Decide, Act” and represent the four components of any decision made and especially those made in a dynamic environment. In a mugging situation, your attacker has already reached the “act” phase – he’s observed his target, oriented himself for max advantage, decided when and how to press the attack and is now on the “act” phase of the attack.
Generally, the act of fighting back in and of itself will interrupt your attacker’s decision making process and force him to do a battlefield risk/reward calculation. The speed at which you react will help that calculation end in your favor. Hypothetically example: you’re confronted by an attacker armed with a contact weapon but initially outside of contact range. He’s in the “act” stage – you observe, orient (filter the information through your training and evaluate the best course of action), decide to draw your pistol, and then act on that decision by drawing your pistol. Because you’ve practiced your draw form concealment, you’re able to perform the entire action above in 1.5 seconds or less. Because your attacker was not likely expecting you to react in such an aggressive fashion, you’ve now changed the dynamic of the fight. Instead of you reacting to his initiative, he’s now reacting to your actions. That’s a much more advantageous position for you to be in.