Regions

Windows Server AppFabric Caching
Regions in WSAF Caching exist to allow a set objects to be searched by tag. This search functionality requires all objects in a region to be stored on a single cache host, which is a potential limit on scalability.
ScaleOut StateServer
Searching by tag is supported by ScaleOut StateServer, but objects do not need to be grouped together on the same ScaleOut host if you want to search for them by tag—ScaleOut StateServer is able to perform a distributed query across all objects on all hosts in the data grid. Regions, therefore, are neither needed nor supported.
[Tip] Tip

In addition to tags, ScaleOut StateServer is able to automatically index properties on your .NET objects. Once indexed, you can query against your object properties using ScaleOut’s powerful LINQ provider.