Discussed ways to improve the current property description with Mark Payne and came up with the following:
The maximum number of threads to use for transferring data from this node to other nodes in the cluster. While a given thread can only write to a single socket at a time, a single thread is capable of servicing multiple connections simultaneously because a given connection may not be available for reading/writing at any given time. The default value is 8—i.e., up to 8 threads will be responsible for transferring data to other nodes, regardless of how many nodes are in the cluster.
NOTE: Increasing this value will allow additional threads to be used for communicating with other nodes in the cluster and writing the data to the Content and FlowFile Repositories. However, if this property is set to a value greater than the number of nodes in the cluster multiplied by the number of connections per node (nifi.cluster.load.balance.connections.per.node), then no further benefit will be gained and resources will be wasted.