Good caching policies is one of performance’s best friends, and it can be your new best friend too. Get friendly with intermediary and browser caches by taking control over your WordPress powered website’s HTTP <code>Cache-Control</code> headers.
This is not a caching plugin in itself, but will enable you to leverage existing standard compliant caching systems better. You can set different policies for different kinds of pages to suite your website’s needs. The Cache-Control for WordPress plugin allows you to set different policies for shared/intermediary and private caches. The plugin sets some sensible defaults for a medium traffic blog that publishes an update or two per week.
You can safely set long <code>Cache-Control</code> times as the <code>max-age</code> values is lowered automatically before a scheduled post is about to be published.
Private pages (logged in users, the admin interface, etc.) will not be cached.
The plugin has <a href="https://www.ctrl.blog/entry/wp-cache-control-documentation.html" rel="nofollow ugc">extensive documentation</a>.

Cache-Control

Configurable HTTP Cache-Control response headers for webpages generated by WordPress.

shawfactor

A <code>304 Not Modified HTTP Header</code> tells your visitors that nothing has changed since their last visit. This is important as without this header visitors may be downloading your webpages from scratch each time, slowing down their experience and your site.
Generally if you do not pass <code>304 Not Modified HTTP Header</code> through your HTTP header, crawlers will fetch your whole website and then compare the content of your site with the already indexed content to check whether anything new has been updated on your website or not. But this process consumes a lot of your server resource and bandwidth.
You can know more about it <a href="http://www.feedthebot.com/ifmodified.html" rel="nofollow ugc">here</a>.
<h4>Before reading any further</h4>
Before reading any further it is important to understand this plugin uses output buffering, in fact the Etag sent by this plugin is a hash of the sites buffered content. If your site uses server side caching this plugin may break the caching functionality. Therefore I suggest that you please make sure you have studied the FAQ, before installation and activation.

LH Add Headers

Adds the ETag, Last-Modified, and if appropriate 304 headers to HTTP responses generated by WordPress for more efficient caching.

Cache-Control vs LH Add Headers