under center and pull everyone into a tight formation, the defense stacks the middle and sells out to stop the expected run up the middle or QB sneak. We see so many failed 4th and short conversion attempts due to the defense pinching down all the gaps and shooting more defenders into the pile than the offense can block or move.

I think its a higher conversion chance to spread the field more on 4th down and have the option of the quick slant to the WR on either side of the ball. If this is executed well it is virtually impossible to stop. I also like having the QB have several options on the throw so that he can dump it off quickly to the RB if the defense blitzes heavily.