It has most successfully been used with 400m athletes. The thought behind it is that by doing a near maximal effort of 30-45 seconds within 45 minutes of the competition you may enhance lactate buffering acutely (a short term affect that will only last within that time frame). The 45 minute time frame is used because it adequately permits the athlete to recover (so they don't race while fatigued) but still permits them to take advantage of this physiological affect. To be honest, I've never seen any published research that specifically looks at this issue but there is some research out there that indirectly supports it (as well as the anecdotal evidence).
At the very least, a maximal effort during the warmup ensures that the athlete is warmed-up….something which many runners do not do well before a competition.