In a Man-To-Man Defense, every defensive player is responsible for guarding a player on the offense. In addition to that they will have a responsibility to slide when a another defensive player is beaten by an offensive player. Overall, man defenses are favored in lacrosse as they allow players to strip the ball and attempt to intercept passes more aggressively, however it can be difficult to recover when a defender is beaten and slide responsibilities sometimes become muddled.
Traditionally Man-To-Man Defense is more aggressive than zone defense. Man-To-Man Defense also allows for specific matchups, where a team's best defender can stay on a player who has to be guarded at all times, whereas in zone defense your best defender is not guaranteed to stay with the opposing team’s best offensive threat.
Vulnerabilities of Man-To-Man Defense are that it allows the offensive team to run picks and screens more effectively, and it leaves weaker or slower defenders more exposed.