I can definitely dig the idea. Even the possibility of certain regions yielding special resources (this is further on, expansion ideas here) for building or researching certain rarer types of units/spells/armors and being able to set up a vast supply chain to utilize it across a large territory.
Something like a guild pushing deep into enemy territory to capture an npc mine, then set up a post of armies to ferry it back to their Strongholds or something of the like.
On the siege idea, smashing supplies on the way to lock someone down would be awesome, but I feel like the enemy army would pound down the gate at this point. I have no idea how often such a stalemate could occur.
On the flip side, it would also be neat to be able to scar some territory in a retreat effort, making the land useless for x amount of hours/days to the person who chased you out of there. Set fire to the fields, make him wait for those resources!