title: Why do you check for savedInstanceState == null when adding fragment?
body: <p>In the fragment <a href="http://developer.android.com/guide/components/fragments.html">doc</a>, in one of the example, they check for <code>savedInstanceState == null</code> when adding a fragment:</p>
  
  <pre><code>public static class DetailsActivity extends Activity {
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
  
          if (getResources().getConfiguration().orientation
                  == Configuration.ORIENTATION_LANDSCAPE) {
              // If the screen is now in landscape mode, we can show the
              // dialog in-line with the list so we don't need this activity.
              finish();
              return;
          }
  
          if (savedInstanceState == null) {
              // During initial setup, plug in the details fragment.
              DetailsFragment details = new DetailsFragment();
              details.setArguments(getIntent().getExtras());
              getFragmentManager().beginTransaction().add(android.R.id.content, details).commit();
          }
      }
  }
  </code></pre>
  
  <p>What is the purpose of this check? What would happen if it is not there?</p>