Plugin provides functionality to cache different parts of the page - from whole page cache to individual object cache. It can reduce page load time and improve visitor experience. Plugin works with various number of technologies and is suitable for different scale installations.
Mainly I use it for those Wordpress site, that are mostly static to provide full-page cache. Additionaly I use it as object cache plugin on shared hosting servers, as it offer simple file-based persistent cache.
Most of all I like ability to use different cache backends - from simple filesystem storage to Memcache and Redis. It can suit and work in any environment and in most cases will greatly reduce page load times.
Not many plugins will offer such wide functionality. In the past months I came across Docket Cache, that offer nice object cache functionality, but can not do full-page cache.
If you have option to use Redis, then Redis Object Cache is a exceptional-speed plugin for object cache.