As in life most people take the low and easy road...they want results but don't really want to pay full price. Who like the feeling of running a 400m flat chat...few are so masochistic. Sure, after the performance, in retrospect you can conjure-up any story you like that it felt great, but that's usually clouted by a great performance result.
In short, it makes no physiologic sense. The results I've and I other have gotten, as well experiments in animals are unequivocal: to obtain your absolute best result, metabolic rate must be close to basal (or below if you know how). To achieve that means: no warm up, surprise (check-out the anticipatory exercise response), very early morning dives (sparrows fart and not after breakfast!), no stretching, no massage. But you've got to be immersed just long enough to shift the venous pool to the lungs. My opinion is that your venous stores, which are comparatively low in O2, and largely reside in the periphery but make up some 2/3 of your blood volume, can probably be arterialized (oxygenated) and enhance you overall blood O2 stores (see the run-in I had with Simon Mitchell years ago); cold-induced peripheral vasoconstriction will help to speed up the process => exposed legs and arms especially. In a nutshell...