title: Best practice for an Xcode project groups structure?
body: <p>In tutorials and examples that provide code samples, sometimes I see that project files in the Xcode's Project navigator are arranged by groups following the MVC pattern ("Views", "Controllers", "Model"), and other times they are organized into groups by functionality ("Login", "Checklist", for instance).</p>
  
  <p>Concerning iOS, is there any Apple's convention/recommendation for this? 
  Which should be the best practice?</p>