title: Mqtt: is it necessary to unsubscribe?
body: <p>If a client is disconnecting, is it necessary to unsubscribe beforehand?</p>
  
  <p>I originally thought it was, but then if a client disconnects unexpectedly, you cannot unsubscribe ..</p>
  
  <p>therefore, unsubscribing is pointless unless you are still connected and no longer want to receive messages ..</p>
  
  <p>Is this a correct assumption?</p>