I love little details in settings that add to verisimilitude. The problem with this predeliction is that when I do my own world building I often let these details bog me down. It's hard to tell what sort of thing is going to add enough to the setting (and play) that it will be a worthwhile investment of creative energy.
One of the things that I like to think about is the economic situations and connections between the communities I describe. But, as Levi of Amagi Games aptly observes, "it rarely makes for awesome play to know that the Sto Lat plains export cabbages and cabbage products".
Detailing imports and exports of a region can have a payoff in creative terms. Knowing that one region depends on another for its supply of iron might inspire political details revolving around this supply/dependence relationship. All too often though such details are just so much baggage, and eventually it stultifies the fantasy elements of a setting when too much has to be "realistic" and work like the world we live in. As one of my players pointed out in a different context (paraphrasing), "it's no fun to play paycheques and pensions".
Levi is good at coming up with little shards of genius, and his latest gambit[1. "Gambit" is Levi's term for a modular fragment of system-independent game rules that can be dropped into an existing system in order to tweak its operation. Check out Event Bounties and Temptation Dice for two interesting examples.], Import-Export, is a good one. Instead of noting what moves between communities, note instead who is being imported and exported.
A city exports faith healers and imports soldier-recruits? That sounds like a pretty awesome expansionist benevolent theocracy, which could be a good shades-of-grey ally or adversary for the player characters. Noting the movement of people and professions says so much more about the social, cultural, or political landscape than does how much silk and silver ore moves around.
See, already I'm having ideas that are directly creative, whereas thinking about commodities exchanges tends to bog me down. I have another idea, but since it's for an imminent plot point in Edge of Empire it'll have to wait a few sessions before it wouldn't be a spoiler...