So Im really big on the "Why's" So lets look at the idea of moving during the draw stroke in the context of a Self Defense situation. The movement is going to be a simple side step,
Reason one to move, Misses
Misses, yea lets hope the bad guy sucks at shooting and is right handed, if this is the case his "Misses" will be to his low left ( we hope) so if we move to our Left we are moving father away from his shots. Now if bad guy is Left handed well ya might want to move to your right. This is of course dependent on your surroundings if you can move, move!!!
Reason two to move, Tunnel vision
Tunnel vision will happen to you under "extreme stress" it will also happen to the bad guy, think about it, he knows what he's doing may very well get in a trip to prison or worse he picks the wrong person to jack up and they shoot him. So bad guy walks up to you in the IHOP parking lot ( that's were it happened to me) and ask's for money you tell him no and to leave you alone and he gets closer( inside about 5yards) and ask's agin, you take a big step to the left in this case and watch his face and eyes look like they just saw a magic trick, you just disappeared... In "extreme stress" your vision will shut out the peripheral and just concentrate on the object in the center field of focus, it's like looking though a straw. So bad guy gets close to you and brandishes a weapon, you side step and draw ( at the same time) and if he's in tunnel vision he'll have to relocate you and this gives you time, and time is what its all about.
So in this type of situation time is king and the more time you have the better, so a fast draw stroke can buy you time, but there are a LOT of other things that can as well. Take the situation that happened to me in the IHOP parking lot, the reason it worked out okay( didn't have to use my gun) for me was I saw it coming and knew what the pre-asult indicators are, as I saw him act them out I knew what he was up to and was able to manage the situation with out having to use my gun and Ultimately that's what were after.