Explanation/Reference: https://docs.splunk.com/Documentation/ES/5.3.1/Install/InstallEnterpriseSecuritySHC

Setting site=site0 on all Search Head Cluster members disables search site affinity. Search site affinity is a feature that allows search heads to preferentially search the peer nodes that are in the same site as the search head, to reduce network latency and bandwidth consumption. By setting site=site0, which is a special value that indicates no site, the search heads will search all peer nodes regardless of their site. Setting site=site0 does not set all members to dynamic captaincy, enable multisite search artifact replication, or enable automatic search site affinity discovery. Dynamic captaincy is a feature that allows any member to become the captain, and it is enabled by default. Multisite search artifact replication is a feature that allows search artifacts to be replicated across sites, and it is enabled by setting site_replication_factor to a value greater than 1. Automatic search site affinity discovery is a feature that allows search heads to automatically determine their site based on the network latency to the peer nodes, and it is enabled by setting site=auto