title: When to use event and command for WPF/MVVM?
body: <p>I am practicing on how to write a WPF application with MVVM pattern. So far I haven't used command in my code. In my Viewmodel I implement <code>INotifyPropertyChanged</code> and used (event <code>PropertyChangedEventHandler PropertyChanged</code>) to fire events. 
  Why do I feel like I still miss some concept of WPF about how to use command?</p>
  
  <p>When is it appropriate to use commands?</p>