The RPG Blog Carnival is hosted this month by Dice Monkey. The topic for the month is Established Settings.
I have used quite a few established settings in my gaming life. For D&D, I've run adventures in Greyhawk, Mystara, Blackmoor, the Forgotten Realms, Dragonlance's Krynn, the City-State of the Invincible Overlord (both the Judges Guild version and the Chaosium one from the late 80s), Bard Games' Atlantis, and quite a few others. I have played Traveller in the Spinward Marches and the Imperium. I've adventured throughout Middle Earth. I've cavorted across the rooftops of Spider Man's New York. For most other games, I used whatever setting was included with the game. Ultimately, though, I've always tweaked and changed things, and all of my campaigns have evolved past whatever the original published setting included.
Most early role-playing games didn't start with any established setting, per se. There were particular ideas suggested by the rules, but nothing was explicitly stated about the "world" of the game. Whoever was running and playing the game was expected to develop their own setting. That changed fairly quickly with the publication of the Blackmoor supplement for D&D, the various supplemental campaign books for Traveller, and other, similar supplements. It was easier to get people to play the game if they did not have to put as much work into it up front. Players could buy the rules, a setting supplement, and an adventure and be running much faster than if they just had the rules and had to create everything else on their own.
It was also easier to create adventures and other supplements if there was a common framework to draw on. With an established setting, all of the common elements are there. Anyone designing an adventure or supplement can assume that players already know the base information in the setting and work from there without having to restate everything. That means there are a lot of materials to draw from when running a game in the setting.
And it was easier to move characters between games if there was that common framework of an established setting. In our games back in the 80s, we moved characters between campaigns fairly frequently among our regular groups. It was easy to do so if the characters were all from Greyhawk, so a lot of the DMs in our group ran games in Greyhawk. A character could easily move between the area around the City of Greyhawk into Furyondy, the Wild Coast, the Cairn Hills, or Verbobonc. So we had DMs running different campaigns in different areas, and our characters would spend money and time moving from place to place to join or leave particular groups.
Finally, in an established setting, it is easier for players to aggregate information over time. Although there have been thousands of pages printed about the Forgotten Realms and Greyhawk, this abundance of information is attractive to a lot of players who feel that they are familiar and comfortable in those places. Common, specific elements like the Green Dragon Inn, Waterdeep, Mordenkainen, Elminster, and so on, give players hooks that are immediately recognizable without a lot of backstory, explanation, or description. They have become common knowledge by their use in thousands of games and publications, and their commonality makes them immediately useful in a game.
If you run your own campaign outside of an established setting, all of these things become harder, and the people playing and running the games have to do a lot more work. There is no common framework that can be assumed, the game master has to spend more time explaining and detailing things about the surrounding world to the players. Frequently this means providing some kind of setting document or info dump to the players to put them into the right mindset to play in the world. Every difference or fantastic element must be explained, and players clue in on the obviousness of these differences. The game master is responsible for creating everything to make the atmosphere as rich as possible, and they don't have the luxury of saying something like "the common languages of the area are all listed on page X of the Cyclopedia."
There are a lot of published materials you can use, if you adapt things from other settings, but you have to do some work to fit them into your world. That means at the very least changing the names of places and people and making sure that it fits geographically and thematically.
Character portability can also be a factor. If you use house rules, variants, or specific items or effects tied to your unique world, it is harder for players to transport their characters to a new campaign. They may have an item or ability that other game masters think is too powerful or too unique to introduce into their own campaigns. Or they may simply be too weird to fit in elsewhere.
Any new player introduced into the group needs to have everything explained to them, and they may have trouble acclimating or accepting your design decisions. Say, for instance, that you don't have any elves in your world but one of your players always plays an elf. You may lose that player unless you're willing to accommodate them in some way.
At the moment, I am running two games. One is my Labyrinth Lord game set in Greyhawk. The other is a game using the Moldvay/Cook/Marsh Basic and Expert rules set in my Coastlands setting. So I am seeing both the benefits and drawbacks of both approaches again simultaneously.
In my LL game, I can rely on a small amount of player knowledge about Greyhawk. What people don't know about the world is easily described or referenced, because there is a ton of information available about the setting. If I need to show them a holy symbol for a particular god, a map of a place, or a picture of a famous NPC, I can normally find one with a quick search. I can grab descriptions and notes from published products to give to the players, and I have plenty of published adventures and supplements to make preparation for the game easy.
On the other hand, I have some constraints as well. Some of the players have expectations about particular things in the world that I have changed. Because I am playing in a time before the Greyhawk Wars, they expect certain things to be happening in the campaign world that may not necessarily be happening or come to pass. One character wanted to play a member of a specialty order of a particular deity's church that he saw described in a newer supplement. Looking at the order, I didn't want to introduce them into my campaign, so he had to adjust his character concept a bit. All of these things have changed the published Greyhawk into my Greyhawk.
My Coastlands setting, on the other hand, is something I am making from whole cloth. I am using plenty of things for inspiration, but nothing goes into the world without some change or reworking. That means that I have to describe everything to the players or they have to discover it in pieces through play.
The way that I've gotten around that difficulty is to have the players enter the Coastlands through a gate with no knowledge of where they are or what is there. They have to learn about the world as I present it to them. That gives me time to develop things as they are needed without overburdening myself and still gives them some richness in play. They find something, I describe it and develop it, and we both add a little more to the world. I don't have a lot of specific information about the world that I can draw on yet, but it will develop over time and with play.
A lot of game masters might be uncomfortable coming up with everything as needed like that, but I am enjoying it just as much as I am running in Greyhawk. Both campaigns have their good things and bad things for me as a DM, and I'm sure my players would say the same. Ultimately, though, we are enjoying playing, and that's what really matters!