The player can send support, specifying the formation when sending support (as well as when sending an attack).
If the player is in their city, their morale gets multiplied by the amount of heroes.
While in their city, the player can defend the city with one army without creating a lot of campaigns.
Unit attacks depend on the number of heroes in an army. The amount of troops being able to attack at the same time depends on the amount of heroes and bonuses from the order.