You can also put items the Blacksmith makes in the Forge (it has an inventory) and when you play your other heroes, they can come and collect it.
Similarly, any hero can put their Mystic Metal Fragments in the Forge inventory for the Blacksmith to use later - same with Mana Stone, Mithral, or any other things they end up with that he can use.
I think potion benches have the same functionality.