If this option is selected, the View will display a list of possible contextual filters that could be used, along with a count of the number of items that would be returned if you were to use that filter. If we wanted to provide a list of users that had edited articles and then allow someone to click on a particular user to see their Articles, this is what we would do. For example, select the following:

This then shows the list of users along with a link that would then provide the contextual filter.