In reply to mark k..

@mark k. - The site owner or site developer should have an idea when a feature is used. There a couple of time where is difficult for the plugin author to know when a feature/shortcode is used. I have not yet found a way to detect if a widget is being used on a page. I can only know if a widget is being used but that could be on any page. Another example is content saved in metaboxes using a plugin like ACF.

It is not a simple as it may seem.