In its most recognizable form, dishonesty, venality causes people to lie and steal for their personal advantage.
Venality in its mild form is a vice peculiar to persons occupied in by government or military organizations. In these, one is supposed to act for honor, not money. This helps assure that the organization can make a lasting settlement of disputes. For people to accept such settlements, the acts of the government must be seen as just. This perception enhances the legitimacy of the government.
In contrast, no one would be surprised to find a merchant or hired person making professional decisions for venal reasons. In some sense, their profession demands venality as a duty. This may be why many militaristic societies despise merchants.