When saving/updating a model you might want to get a JSON response that includes some relationship data as well.
public function store()
{
$inputs = Input::all();
$post = new Post;
$post->fill($inputs);
// Here we add the many to many model ID for he relationship
$post->user_id = Auth::user()->user_id;
// Now by calling the relationship we can make sure that the user data will be present in the response
$post->user;
return $post->save()
}