It's roughly the military equivalent of the enemy having their artillery emplacements overrun and then turned against their own troops. Size of the respective fighting forces is irrelevant, it's simply a useful tactic. Of course if the overrun emplacements were part of a large, belligerent force agitating a smaller force without cause, there may seem to be a certain justice in using their weapons against them. It doesn't make the subsequent killing "good", but it may help discourage further aggression against strategically disadvantaged but tactically superior forces.