This is a simple technique to prevent sessions timing out on remote nodes when they are still active on the main node.

Not allowing session to time out prematurely is important to ensuring there is a proper backup of the session.

It is particularly important in the case of AttributeBasedClusteredSession. In that case, separate nodes are created for each attribute. If a session expires on a remote server, all attribute nodes are evicted. If the session is later modified on the main node, the sessin metadata and the modified attribute will be replicated, but other attributes will not. So, if there is a failover there will be missing attributes.