Parameter elements include many different input types. The text type provides a textarea where one could enter raw HTML, but since Joomla! has a built-in method for calling a WYSIWYG editor...why not use it?
When editing an item within your application (component, template, module, etc...) you may be away from the editor form for a period of time doing research, or whatever. It's always a pain to find that when you return to your form, finish filling it in and click the submit button - Joomla has logged you out and your input has been lost.
This element implements the Joomla! AJAX keepalive behavior to prevent that timeout.
