When the defense is used against lower-rated opponents, it often occurs that White possesses little knowledge or has few concrete ideas about how to play against it. Black is unlikely to gain an advantage out of the opening, but if White simply drifts along without a clear plan, Black's counterplay can develop quickly. This game is an excellent illustration of this, as White allows Black to equalize early on, then never really seems to develop a plan of his own. The one concrete idea he plays on moves 23-24 simply leads to better play for Black. By move 31 Black is ready to attack and seven moves later White is mated.
While there were a number of instructive improvements for both sides along the way, the overall development of the game shows how Black can effectively neutralize White's opening play, improve his position, then quickly go over to the attack when an opportunity is given. This is especially dangerous against lower-rated players who lack the experience or understanding of White's more complex ideas. Black's position is both simpler to play and has latent attacking resources that the patient player can reveal later in the middlegame.