That grip is most appropriate for rapid transition shooting as it allows for greater muzzle control and limits some of the overtravel when acquiring your target.
IF you unlock your elbow and relax your shoulder. If you don't, you have to turret your entire upper body to transition every time which is slower and more prone to overtravel. (Sometimes you have to turn your entire upper body. For smaller transitions, you don't. And shouldn't.)
Example: Miculek running a V-drill with a Barrett .50. So---transitions and serious recoil control needed, and yet, he doesn't lock out his elbow and shoulder. Now, Miculek is a freak of nature, but still....if he doesn't lock it out for a .50, then chances are you won't need it for a .223.
And more importantly, if your upper body isn't locked, then you'll be able to move faster. If you watch Miculek and some others shooting REALLY fast, you'll see that their off hand is way out there, but they don't do the forward shoulder roll and full medial flexion of the wrist that Costa (and LOTS of "operators", plus a few other 3-gunners, true) use. Hand forward, yes. Extended, yes. Wrist driven out so far that the elbow locks---no.
See Miculek, Butler, Garcia, Laker, Upchurch, etc....
What they do is extend the wrist so the index finger points inline with the barrel. We point instinctively well, so that helps transitions. Hand is still in an extended position to control the front of the barrel---but the wrist/elbow isn't locked, and the shoulder isn't rolled forward to slow you down for no reason.
A good example of it is shown here, with champion Keith Garcia doing some Airsoft practice.
General concept: if you have locked joints and need to move more mass to shift point of aim, you are going to be slower. The only reason to do so (and take the "slow" penalty) is either to 1) handle recoil (and that is a bad way to handle recoil), or 2) lock the body for stability when extreme precision is needed.
Shooting a .223 most of the time requires neither of those---and when it requires the second, you normally have something to brace against. (The ground, a wall, a post---something.)
Sure, some people can do that and still be fast. Of course, if they'd put that much training and practice into doing it the other way, they'd be even faster...
IMO, of course.
