True enough: Building your own world will take more time out of your already busy game-mastering schedule. And note that nothing here is a criticism of commercial settings. But building your own world does afford benefits that using a commercial setting does not.

If you’re reading this, I’m going to make some basic assumptions:

You’re Playing a Fantasy Roleplaying Game

Building a fantasy world requires a degree of effort not required for games set in other genres: Sci-fi game worlds have different requirements, as do worlds for the modern, horror, and historical genres. As a result, the world-building process for fantasy games is composed of different steps and a different level of detail.

It doesn’t matter what fantasy game you play–in most cases, a fantasy world is agnostic with respect to the game system used. What does matter is that the flavour, populations, creatures, magic, and technology of your game fit one of the “standard” fantasy genres.

You’re a Game Master With Creative Ideas

It goes without saying that gamers are creative and imaginative folk, and this is doubly true for game masters. You probably have a library of treasured fantasy novels, movies, and maybe comics, all mixed with a healthy dose of historical knowledge and resources. As you read and watch, new ideas spring up–character professions, social hierarchies, monsters, religious cults, non-human races, special abilities–and you find yourself wondering how to add them to your campaign.

The task shouldn’t be taken lightly–it’s very easy to spawn chaos out of order, and blithely adding a hodge-podge of good creative ideas can result in a campaign that’s hard to justify. Why justify a fantasy world? Because your players need to suspend their disbelief to enjoy it. Because you, as GM, need to understand how all the elements interact to trace a believable line from cause to effect. Though it may not be immediately apparent, a campaign lacking internal cohesion is fragile and will eventually break.

You Need a Unique Environment to Cultivate These Ideas

There’s an assumed disparity between a commercial setting and a creative GM. Simply put, commercial settings–often written with a particular game system in mind–possess an internal cohesion that suffers only a certain amount of modification before breaking. In other words, your creativity as a GM is bounded by the creativity already applied by the setting’s author. Consider some examples:

• You’re running a game in Middle Earth, but you have an idea for a religous fighting order; since gods and priests are notably absent from Middle Earth, adding your idea seamlessly will be hard.
• You’re running a game in Greyhawk, and you’ve successfully built a dynamic campaign; unfortunately most of the changes you’ve made are undone with the publication of From the Ashes.
• You’re running a game in the Forgotten Realms, but don’t like the idea of drow elves under every rock; replacing the drow with another evil racial type, or ignoring the archetype completely, will contradict the setting’s flavour.

It’s true that you could still use these worlds and include your own ideas, but there’s work involved. Arguably, expending such effort defeats the purpose of using a commercial setting in the first place: If you’re taking the extra time to make the setting fit your ideas, that’s a good point in favour of building your own world.