The training effect of the flying sprints can be two fold:
1: The increased capacity for 40y by increased high speed distance tolerance (single and multiple), stretching the energy envelope just to the right of the event itself.
2: The increased capacity for 40y by increased speed, stretching the EE just to the left of the event itself.
While both can play a role, 2 will be far more important, especially for the big guys, because:
A: top speed occurs well within the 40y run itself, directly affecting the time, while backs may achieve top speed beyond the 40y mark therefor affecting performance indirectly.
B: Power will always predominate over SE with both groups but especially with the big guys.
So often the big guys are subjected to gassers which I find counter-productive.