What about...repair costs? Lower pay for troops away from home (since they can loot in their spare time!)?
That's interesting. Afaik, armies were often kept in the field with the spoils of war. This would make war less expensive. Also, it would mean mockery wars, meaning simply being at war without any actual fighting), would not gain any bonuses.
Of course, those extra incomes could be used to strengthen the armies beyond the limits of the realm income, providing a bonus in fighting strength as well.
