T5 Hide dead menu metaboxesWordPress Plugin to improve the menu management screen.

hide-dead-menu-metaboxes.php

<?php
/**
 * Plugin Name: T5 Hide dead menu metaboxes
 * Description: Do not show menu metaboxes when no nav menu exists.
 * Plugin URI:  https://gist.github.com/thefuxia/4432959
 * Version:     2013.01.02
 * Author:      Fuxia Scholz
 * Author URI:  https://fuxia.me
 * Licence:     MIT
 * License URI: http://opensource.org/licenses/MIT
 */

add_action( 'admin_head-nav-menus.php', 't5_hide_dead_menu_metaboxes' );

/**
 * Remove metaboxes for menu items when no menu exists.
 *
 * @wp-hook admin_head-nav-menus.php
 * @return  void
 */
function t5_hide_dead_menu_metaboxes()
{
	if ( empty ( $GLOBALS['nav_menus'] ) )
	{
		$GLOBALS['wp_meta_boxes']['nav-menus'] = array ();
		echo '<style>#nav-menus-frame{margin-left:0 !important;padding-top:20px}</style>';
	}
}