The thing I don't like 3 players on one side is that it has a critical flaw in the flanks. If the opponent plays defensive down flank the chance creation ratio (CCR) will be horrible.

Even more significant if the formation is asymmetric and 3 player on only one side, I've exploited this weakness many times and it usually provide a CCR exceeding 60% in my favor.

CCR is Attack : Defense in a game your team performed (success or not in those attempts are irrelevant), in rare cases this can exceed 2:1. Obviously the higher number of attacks your team make the better chance to win. This factor is mainly dictated by formation and orders.