Honor improves the effectiveness of one's army in a variety of ways.
Adopting Honor gives a +33% combat bonus VS Barbarians, and notifications will be provided when new Barbarian Encampments spawn in revealed territory. Gain Culture for the empire from each barbarian killed. Unlocks building the Statue of Zeus.
Adopting all policies in the Honor tree will grant Gold for each enemy unit killed. It also allows the purchase of Great Generals with Faith starting in the Industrial Era.
In an "honorable" society, the citizens' status is based upon the society's judgment of their personal qualities. Qualities that are usually considered honorable include fealty, honesty, integrity, and courage. In many such societies men are expected to "defend their honor" to the death, as any loss of honor is considered far worse than loss of life.