curious about code in the upload module

I'm curious about this piece of code in upload_js() in the upload module:

  if(!empty($form_state['values']['files'])) {
    foreach ($form_state['values']['files'] as $fid => $file) {
      if (isset($cached_form['#node']->files[$fid])) {
	$files[$fid] = $cached_form['#node']->files[$fid];
      }
    }
  }
  $node = $cached_form['#node'];
  $node->files = $files;

What does this do, exactly? Since just before this we call upload_node_form_submit() which adds the most recently attached file to the node thus:

    $form['#node']->files[$file->fid] = $file;

The block of code in upload_js seems redundant to me, but obviously I'm missing something.

This is in no way a bug report, I'm just looking for a little education, so if somebody can take a stab at explaining what is going on here to me, I will appreciate it!