This allows third-party services greater access to your website: If you want to add Open Graph information to your website, or verify your website with Google or Pinterest, the meta tags that they provide will be placed in this area.
Examples of correctly-formatted meta tags:
<meta property="og:title" content="The Invention of Morel" /> <meta property="og:image" content="http://upload.wikimedia.org/wikipedia/en/c/ca/Last_year_marienbad.jpg" /> <meta name="robots" content="NOODP">
Avoid placing keyword and description meta tags into the "Additional <meta> tags" area. Google ignores keyword meta tags for ranking, and may in fact down-rank your website for having too many keywords inside it. Cargo already provides fields for adding for description and keywords meta tags into your website, also in the Site Details area. For more information, see Search Engine Optimization (SEO).
Ensure that each of your meta tags are correctly formatted, or they may display as plain text in your website or interfere with normal website functionality, or not work as intended. More information on formatting tags is available at the Mozilla Developer Network.