Welcome that new feature, Sharepoint!
The distributed caching is used by SharePoint 2013 for caching social elements and FedAuth tokens. Every time a user accesses a front end server the user needs to be authenticated which can become an issue when using multiple front end servers. In SharePoint 2010 this was handled by enabling load balancing affinity (Sticky Sessions) to ensure that the user stayed on the same front end server. By caching the FedAuth token in the distributed cache it is no longer necessary to enable sticky session since the authentication token is now available from all front end servers through the cache cluster.
Prerequisite: Windows Server AppFabric cache service
Great article on AppFabric: http://mysharedpoints.blogspot.hu/2012/08/appfabric-distributed-caching-and.html