WP Rocket is a premium caching plugin developed by WP Media. Years ago, the caching plugin market was dominated by free plugins from the official WordPress repository, most notably by W3 Total Cache and WP Super Cache.
When WP Rocket was launched, some people were skeptical about its future. A caching plugin without a free version? Can it work, can it be successful? It's not even a freemium plugin, the only way to get it is to pay for a licence. Will people trust it if there are already enough free caching plugins in the official WordPress repository?
Apparently, many people have trusted the developers of WP Rocket. Today, it is one of the most popular caching plugins for WordPress, despite not having a free version. It does not have as many features as W3 Total Cache, but it does have pretty much all the features that the average WordPress website needs. And the features offered by WP Rocket work remarkably well.
The lack of features is not a weakness of this plugin. On the contrary, WP Rocket is much simpler to configure correctly than e.g. W3 Total Cache and it simply works. It covers the needs of most WordPress websites. The focus is not on the number of features, but on stability and the ease of use.
The plugin generates page cache (HTML) and offers a number of useful speed optimization features. The HTML cache can be preloaded, which is a must for larger sites and for sites where the cache must be purged on a regular basis. Without preloading, cache would be generated only when a visitor opens an uncached URL. Cache purging and preloading can be scheduled or triggered manually, which is very convenient. In the plugin's interface you can observe the preloading progress by refreshing the page.
As some other caching plugins, WP Rocket can optimize (minify and concatenate) .js and .css files. Your mileage may vary, however, I think that Autoptimize does a slightly better job at that. I use WP Rocket together with Autoptimize and they complement each other very nicely.
The plugin can lazy load images, iframes and videos and I think it is very good at that, at least as far as images are concerned. The developers have released also a separate plugin with only this functionality. It is called Lazy Load – Optimize Images and can be used with other caching plugins. It is available for free from the official WordPress plugin repository.
All in all, WP Rocket is a very solid caching plugin. It might not have as many features as some of the competitors, but if you configure it properly, it will definitely help you speed up your WordPress website.