What mainland regions that are themed?

[Shhy]

What mainland regions are themed? Is there an advantage to a themed sim?

[SAULGOODiE]

Shhy, nowadays Mainland Themes are more loose guidelines than anything. There are still some places such as Bay City which mainain the theme Linden intended, but on the other hand entire continents such as Sartori were originally Japanese themed, but over the years has just devolved into randomity. 

Private sims are the most popular use of theming, advantages can range from having a cohesive enviroment for photography, to gathering like-minded folks together to roleplay things such as Science Fiction or Modern Suburban Life. There are Sims that exist on the mainland that maintain themes, but rarely do they stretch more than 1 or 2 sims continually. 

Some "Sub Continents", or smaller mainlands, do exist that still implement and maintain their themes (e.g. Caledon, Winterfell, Babbage), but more often than not it is a simialr situation to what I stated above. The advantages are going to be entirely up to the theme itself and what activities take place on the sim. It can be quite rewarding to be a part of a themed sim community that is in line with your interests and values.