It is clear now that what a fictional setting requires to make it suitable for storytelling is not what makes it suitable for gaming. Often those requirements are in conflict, as we see when a fictional setting created for one purpose (e.g. Forgotten Realms, Greyhawk, Dragonlance) are used for the other. I'll tackle setting-for-story at the Study; here I'll tackle setting-for-gaming. Specifically, I'm talking about setting-for-tabletop RPGs.
The distinction begins with the approach. Ignore the commercial settings; they're done that way for reasons that have far more to do with commercial necessity than practical use at your table. Application for gaming purposes requires that you start small and build out only as play requires. Ray Winniger nailed these as "The Seven Rules of Dungeoncraft" during the waning years of Dragon Magazine's run as a proper print magazine.
- Never force yourself to create more than you must.
- Whenever you design a major piece of the campaign world, always devise at least one secret related to that piece.
- Whenever you have no idea what the probability of success should be for a particular situation, consider it 50%.
- Always challenge both the players and their characters.
- What's done is done.
- Simple, easily identifiable characteristics are the best tools for portraying NPCs.
- Running a good campaign is about building a world, not building a story.
What I posted yesterday conforms to these seven rules. Having a monster palette in place acts as a creative component to inform my creative decisions down the road, when your campaign play requires that you create new content for the players to engage. That's how you make a setting work in gaming. You do it as required, taking the current state of what's been done and iterating out a plausible expansion given both the present state and its current momentum.
Yes, this applies to your Star Wars game. You don't make shit up until you need to, using what's there and what's gone before to inform that creation. This applies to your Traveller game; don't touch those tables until you must. This applies to your Robotech, MechWarrior, Call of Cthulhu, RIFTS, TORG (yes, even that game) and so on- all proper tabletop RPG campaigns work best when done this way.