Most sites contain areas of text and HTML that are repeated throughout the site. Links in the footer, copyright information, a button or phone number in the header, or some other static content. If you're a developer working on your own site, then you may just keep this in an include file and edit the code manually. If you're using Wordpress as a CMS for a client, then it's a good idea to make these areas of text/images editable, so that they can have full control of their site.