Custom fields of pages
You can use custom fields for pages to add additional information to a page using user-defined fields. You can use these fields for grouping pages by some classification, such as tag, so that a user can filter which pages are shown in the navigation. You can, for example, add images for the pages in your navigation. Another useful scenario is when you want the pages to be integrated with Facebook Open Graph giving the user the ability to control how the page is shared in Facebook. Same scenario is applicable to Twitter and Twitter Cards.