When to Use Full-Page Caching
A site with full page caching activated can handle many times the traffic of a site with no caching. When your site is linked by a major news site, you need to be prepared to deliver thousands of page views per minute. Without full-page caching the requests will end up in a queue, resulting in a site that responds slower. Full-page caching is often used to speed up sites, which it does, but you will not be able to cache all pages. For this and many other reasons, you should only use full page caching to scale your site, not to speed it up.