Your website probably uses lots of static files. Image, Javascript and CSS files are usually static files that could just as easily be served from another site or CDN. Therefore, this plugin replaces any links in the <code>wp-content</code> and <code>wp-includes</code> directories (except for PHP files) on your site with the URL you provide below. That way you can either copy all the static content to a dedicated host or mirror the files to a CDN by <a href="https://knowledgelayer.softlayer.com/faq/how-does-origin-pull-work" target="_blank">origin pull</a>.