The key benefits of a multi-server (master-master) setup are as follows:
The master-master setup is useful in cases where you want to set up two separate servers for two separate and unrelated sets of users. This setup is similar to two separate single-server setups.
The master-master setup limits sharing to a set of related users.
This configuration is most suitable when an organization has more than one identity pool.
In an organization with a single identity tree, this configuration allows a particular domain to be part of the Business Continuity Clusters (BCC) for data replication and high availability.