Speed Up - Page Cache was constructed for made caching dead simple. Simple one-click install. That's it.
When a page is rendered, php and mysql are used. Therefore, system needs RAM and CPU.
If many visitors come to a site, system uses lots of RAM and CPU so page is rendered so slowly. In this case, you need a cache system not to render page again and again. Cache system generates a static html file and saves. Other users reach to static html page.
After a html file is generated your webserver will serve that file instead of processing the comparatively heavier and more expensive WordPress PHP scripts.
The static html files will be served to the vast majority of your users:
- Users who are not logged in.
- Users who have not left a comment on your blog.
- Or users who have not viewed a password protected post.
99% of your visitors will be served static html files. One cached file can be served thousands of times.
In addition, the site speed is used in Google's search ranking algorithm so cache plugins that can improve your page load time will also improve your SEO ranking.