I'm a fan of multiple worlds/settings for D&D/PF. 3.5 had Greyhawk, Forgotten Realms, Eberron, and Dragonlance. Each setting had its own style and power level. Greyhawk was the core setting and worked well for medium and low power/medium and low fantasy and worked okay for high fantasy. Forgotten Realms was better suited to high fantasy, and had a lot of variety (standard medieval Europe inspired fantasy to desert campaigns to South American to Oriental Adventures). Eberron was a unique setting with lots of cool stuff unique to Eberron. Dragonlance is one of my all-time favorite settings.
Each setting had its own prestige classes, more or less balanced within that setting. Some had their own pc races balanced within that setting.
So are there any downsides to having multiple interesting settings? Any reason not to have more than one setting?
