Extensions are installable packages which give CiviCRM new functionality, and this directory provides a centralized list of extensions which the CiviCRM community has created.
This listing displays CiviCRM extensions that work on all Content Management Systems (CMS). You can also browse directories of plugins or modules that are made specifically for Backdrop, Drupal, Joomla and WordPress. View newest extensions. There are also many more extensions in various stages of development available on CiviCRM's Gitlab.
Create custom searches with optional the possibility to export the results
Create an API to fetch data. This is quite useful if you have external systems which need data from CiviCRM.
... and developers can enhance the outputs of the data processor so that much more is possible, even things we haven't thought of yet.
For example if it is installed on a CiviCRM system it will minify crm-menubar.css. If Stripe is installed it will minify stripe css/js.