Drupal has a built in Cache API, which allows module developers to save output of the expensive parts of code to be re-used in future. This not only makes code faster and more responsive, but will also save a lot of server resources.

The result of proper use of Drupal's caching mechanisms will result in more satisfied users and substantial savings, caused by lower hardware requirements.

Drupal's cache API is really easy to use, so every developer should use it. You do not know how to so it? Come to this session and you will find out!