How is it different from protecting a 1 goal lead in the last 10 minutes? Team bunkers, but then the attacking side gets a lot more chances at the goal! And if they score, now they will win the game because they win the extra time, which shifts the balance... no tie possible so one side MUST take chances!
The theory is to take the KFTPM before the extra time, not the match. It reduces this bunker down idea. But if you've had a 0-0 snoozer already, making one team attack for it might just make the game more exciting in the finish.