title: rails routing member and non-member nesting
body: <p>Two quite similar routing settings really is confusing.</p>
  
  <pre><code>resources :authors do
    resources :books
  end
  </code></pre>
  
  <p>and</p>
  
  <pre><code>resources :authors do
    member do
      resources :books
    end
  end
  </code></pre>
  
  <p>As we all know, rails will generate the following routings :</p>
  
  <pre><code>writer_book   GET  /writers/:writer_id/books/:id(.:format)   books#show
  </code></pre>
  
  <p>and</p>
  
  <pre><code>book          GET    /writers/:id/books/:id(.:format)        books#show 
  </code></pre>
  
  <p>How is this member option useful? 
  One can just not using member option and set params[:writer_id] in books_controller and  be done with it right?
  Does this will have a bad affect when the application gets bigger? What are the consequences?</p>