Joomla have a native cache and Gzip compression system, that's a good start. Speed Cache comes over as a natural improvement of the Joomla page cache system with a lot of performance, compatibility and features enhancement. To be more specific Speed Cache brings: a powerful static page caching, compatible with user sessions, a full browser cache system, a preloading cache system, URL inclusion cache control and resources group minification. Some handy tools are also part of the extension like the activation for logged in/logout users, an auto-index for caching URLs and an automatic cache cleaner on specified actions. Everything is under control from the Speed Cache dashboard.