Bob the Fighter is using a Maul of the Titans and has the Greater Sunder feat.
Maul of the Titans: This mallet is 8 feet long. If used as a weapon, it is the equivalent of a +3 greatclub and deals triple damage against inanimate objects. The wielder must have a Strength of at least 18 to wield it properly. Otherwise, she takes a –4 penalty on attack rolls.
Greater Sunder: You receive a +2 bonus on checks made to sunder an item. This bonus stacks with the bonus granted by Improved Sunder. Whenever you sunder to destroy a weapon, shield, or suit of armor, any excess damage is applied to the item's wielder. No damage is transferred if you decide to leave the item with 1 hit point.
Let's say that Bob is a level 8 Fighter, with Strength 22 (+6) and Power Attack, Improved Sunder, Greater Sunder, Gate Breaker.
Sunder Damage with Two-Handed Maul = 1d10+27 [Strength +9, Power Attack +9, Gate Breaker +6, Maul Enhancement +3].
He Sunders a shield with hardness 10 and 10 hit points (let's assume he rolls max damage) for a total 37×3 = 111.
Does the wearer of the shield take 91 damage (111 − 10 hardness − 10 hp)? That is way more damage that Bob could inflict with a regular non-critical attack to the target's face.