title: up() and down() versus Ext.getCmp()
body: <p>I'm very confused which one I need to use for grep object between up() down() and Ext.getCmp(ID).</p>
  
  <p>For me, it is easier that define ID to object and retrieve the object by Ext.getCmp('ID')
  and the code looks more clean.</p>
  
  <p>For example:</p>
  
  <pre><code>console.log(this.up('panel').up('panel').down('grid'));
  console.log(Ext.getCmp('myPanel'));
  </code></pre>
  
  <p>which one is better for performance?</p>