Why do you need a plug in to cache your users visits in WordPress? The reasons are many. Here are a few;

1) It will save you money on hosting.
2) It makes your site load faster.
3) It will reduce the load on your server.
4) It can help prevent your site from going down during high traffic.

WP Super Cache (by Donncha O Caoimh) is updated often (most recently just 26 days ago), its a great supported wordpress plugin that EVERY WordPress blog owner should be using.

As your WordPress blog generates more traffic you will need to address caching, so before your host calls you to do so, simply go to Plugins -> Install new and search for ‘WP Super Cache’.