This information is part of the Modelica Standard Library maintained by the Modelica Association.This model is the simplest implementation for a splitting/joining component for three flows. Its use is not required. It just formulates the balance equations in the same way that the connect semantics would formulate them anyways. The main advantage of using this component is, that the user does not get confused when looking at the specific enthalpy at each port which might be confusing when not using a splitting/joining component. The reason for the confusion is that one examines the mixing enthalpy of the infinitesimal control volume introduced with the connect statement when looking at the specific enthalpy in the connector which might not be equal to the specific enthalpy at the port in the "real world".