title: What is the clientID needed for?
body: <p>Since specifying the <code>clienID</code> is only a feature in the class <code>MqttAndroidClient</code>, and can not be specified when using classes <code>IMqttClient</code> and <code>IMqttAsynchClient</code>.</p>
  
  <p>what is the real purpose of connecting a client with a unique <code>ID</code>?</p>