Re: quickness & accuracy
I think one way of seeing what these drills do is to just stand there and let someone go "ballistic" on you. Have a friend stick some gloves on and tell him/her to just go for it - making sure they are striking from within hand-weapon range. Then note of how we tend to duck with our head down, close our eyes, look away, just stick our hands up with no rhyme or reason, etc. The guy in the video is doing this all over the place. It's the pressure of the barrage that does this - in combination with our lack of skill in facing such things. To respond in an educated way to such tension, one, in my opinion, has to be "pressure tested." In pressure testing ourselves, we should realize that there are folks out there (e.g. boxers, wing chun practitioners, karateka, kick boxers, etc.) that possess many skills to make it seems as if we are standing still. If we are skilled under such pressures, when we do add our movement to the fray, we can actually use their tendency to cut off angles against them (via irimi and tenkan) - as an example of what one might do.
The drills are also a great way of understanding te-sabaki at a whole other level. That's always a plus as well.