I was reading Noism's (Monster & Manuals) 8th deadly sin of world building a commentary on This io8 article when I discovered replies have an upper limit.
About the only qualm I had when I looked over the article was "explain," as I feel the need to explain why your world is a coherent whole is quite often over-rated. The stupidest point in every zombie movie is when the small town science teacher explains where the zombies came from. We live in an age where multiple game changing discoveries are made every year, but the average consumer reads more about the health benefits of chocolate than they do about the domestication of corn. Yes, I may have enjoyed the geekiness of the Silmarillion. If it had never been published, it would not matter at all in a debate of whether Rings is great. It is Tolkien just showing you how he did the magic trick. Reading Lord of the Rings, you're just impressed by his elvish, the appendixes just explain why you're impressed. Ernest Hemingway wrote that a good story is like an iceberg in that 90% is never seen. It's not that you need to let them know why the world is the way it is, they just get that it is cool.
I admit it. I'm a world builder and an obsessive about it to a point. Mostly because I think the human brain can pull patterns out of seemingly random information or even lacking a real pattern invent a pattern. So a "logical" world is more satisfying to a player than an illogical one, because they recognize it at a nearly subconscious level. They're still apes processing a world of sensory patterns sorting for when they should fight or flee.
I'm always disturbed by the Ogre who is sitting in a room he didn't lock, who is there 24-7. Which is why I, as the GM, put a key in his pocket and know he spends quite a bit of time roaming the city's sewers hunting rats, albino alligators, and the occasional street urchin. Now I might bend the rules to have him in the room the first time the party comes by, but if they flee, he might very well be out next time. I never bother to explain any of this to the party, other than that key and his alligator loin cloth,I just have it to rub that bump in my brain. I've trained my players to look for back exits, which often influences their tactical decisions. I'm not against a bull shit explanation where I use magic like they use science in original star trek, to explain everything away, but I try to save that for emergencies.
Or that Froghemoth (it's frog, it's a behemoth, it's frogHEMOTH!)who occupies that cavern and snatches the occasional errand running orc who works for that wizard who's lair the party is stalking, well he can't live on just what walks by, so somewhere there is a underwater passage which leads to a vague underwater passage section in my mind. It's just a thread hanging off the map, until someone comes up with water-breathing potions.
The kingdom of the mushroom people include nurseries, which is why they keep making a comeback when the party doesn't finish them off and then leaves for six weeks. In contrast the Uruk-hai kingdom it abuts if left alone for six weeks after they kill it's leader and slaughter the cream of it's royalty collapses and becomes a hunting place for beasts.
My first attempt at city building put it in the middle of a wilderness for really no reason. My second one put it on a cliff edge, with a ramp, the choke point for travel. The latest one is a nexus of trade routes, geographical and political, as I felt I need to have a reason for all those buried ruins. I even found myself sketching out things like water levels one day, easily one of the silliest things I've ever spent time on. Well except it allowed me to wing an entire subplot, when a player who'd discovered the joy of rock to mud and mud to rock started running shafts to avoid problems. My city now has a sewers department.
I guess the point I'm making here is that world building is how you get themes. World building allows you to improvise that evening, because you've already thought about the big picture.
Some of that is just me. What I need to consider to get joy out of the game. The pleasure that makes me spend time outside the playing sessions (the GM is the only one who does homework) Some of it might be the audiences I've played to over the years, which affects your style. I've been lucky and I've been cursed to play with some very bright boys and girls. That engineer who knew off hand the weight of a cubic inch of iron and proceeded to do the calculations for what the giant iron doors actually weighed when the party wanted to move them and the calculations as to what a solid silver idol might weigh (make it silver plate, because they'll figure a way to move it, the greedy bastards). The history and anthropology grad students who expect a coherent back story and enjoyed sifting myths for leads. The type of people who realize that GRR Martin isn't a linguistics professor and while they accept it, do recognize that he's absurdly well versed in medieval politics and customs and love him for it.
Now comes that part where I totally contradict everything I've said and argue against the points I just made. That said, I've built a lot of worlds for which I'd just sketched out bare boned themes. It's a plains native world. It's an abandoned, creepy Babylon deity world. It's a robot world. It's a world who's architecture is vaguely reminiscent of Marvin the Martian cartoons. Being an obsessive world builder I once felt the need to build a multiverse of worlds, an effort which quickly got out of hand, as the point was to give them no stable footing, no stable theme. It was open-ended enough (and experimental enough) that they'd often arrive on a world where all I had going was "only invocation spells work, but they're ten times as powerful."
I'll also admit that to run a medieval system requires you close your eyes to a lot of logic, when that medieval system includes magic. Here's one prime example. Every game has castles. Yet these castles are invariably built by morons and I don't mean the morons that decide to stick a thirty story tower in the center. I mean the morons who never consider the technology they have, that is magic. Medieval design is useless against mages. A mage can shoot a fireball through an arrow slit into a ten foot high guard room, where it proceeds to flame the entire garrison. Mages can fly, thus they're air power. Mages can shoot a lighting bolt to bring down walls and stone walls are very expensive to build, which is why we stopped building them after gun powder. Truthfully, a high magic world's fortifications should look more like modern ones, than medieval ones. Yet other than dedicated sand table gamers, who'd enjoy that? Yes there has to be a suspension of logic to run a high magic medieval world.
So having argued both sides of the argument, I feel the need to spend some time sketching in the idea that my city's grain silos are protected by a colony of brownie;s who raise riding ferrets. I have no idea when or where that my come in handy, but it's such an absurd idea, I can't help but think it may come in handy some day.