This plugin uses WordPress + Varnish and caches the sidebar with ESI.
The worst queries in WordPress are usually contained within the sidebar. If your content is engaging and someone browses from one page to the next, most caching plugins need to generate the page and sidebar on a fresh visit. Since this plugin caches the sidebar separately using ESI, the only queries executed on the second and successive pages is the page content - not the sidebar.
WP Greet Box and WP Post Views are known to break with caching.