Register new menu locations right from the menu screen. Never write register_nav_menu again and keep your functions file clean!
Menus Manager is added to the 'Appearance -> Menus' section of your dashboard. From here, you can create a new menu, view your current menus and ids for use in
wp_nav_menu, and delete menus you don't use.
You can hide the Menus Manager using the Screen Options twirldown menu. This is great so that you (or your clients) don't accidentally delete menus.