title: What is the difference between postUpdate and sendCommand in openHAB
body: <p>In a rules file in openHAB I can execute <code>postUpdate</code> and <code>sendCommand</code>. What is the difference?</p>
  
  <p>I noticed, that when I use <code>postUpdate(zwaveLamp1, ON)</code>, only its value is changed, no actions are performed - the light stays dark. <code>sendCommand(zwaveLamp1, ON)</code> will perform the bound action and switch the light on and the item is updated.</p>
  
  <p>Whats the use case of <code>postUpdate</code>? What is it good for?</p>