As a developer, sometimes you need to get into a hard code. This web part allows you to call a static function (and if needed return/render content) quickly, without the need of adding a .aspx+portal template or a "empty" repeater to call a function in the transformation. This Web Part simplifies the process and also allows rendering the content as output, an API (w/content type) or as a File.
This web part can be placed on any page, and allows you to call a named function in it's class. It is useful to perform more advanced actions when a user visits a page, or perhaps you wish wish to output some content that cannot be easily generated through existing web parts (like integrations with 3rd party services).
The web part allows you to return content on the page, or allow you to define the output as the only content (turning the page into an API, feed, or File).
Since this is a web part, it will execute the function whenever the web part is rendered. If your code requires you to perform actions on the Pre Render of a page, or in earlier stages, this may not be of help. This is primarily to allow APIs to be generated that require more complex back end code.
If an API can be generated using a Repeater, Custom Data Table, etc. Please see the Webpart to API Converter web part on the market place.