Robbing carts gives honor. Prince Charming, you don't have to escort carts for honor, so long as they arrive. If they get robbed, they still give honor, just less.
But better to escort them, because if robbed it gives twice less honor.
It usually gives 10-15 carts a day, which provides around 700 honor (or less depending on castle lvl), and if they are robbed, you lose 350 of it
Well not that much, but still... some servers don't have anything except carts, with all dominating kingdom.