How do you choose between "trading" a good (locally) and shipping it (abroad) when the two actions have rather different reward structures?
How do the relevant roles you might play (craftsman, captain, trader) affect these choices?
Of course, if you have a warehouse, that gives you a wider choice of whether to trade or ship, and whether to do so this turn or in the future. More to the point, how do you decide, "I need to buy a warehouse THIS turn, for 1-2 turns down the road?"