This chart helps you anticipate when leads will have/have had exhausted all the nurture content. The graph is set immediately after each cast. The example below shows that in last cast, 2 leads have exhausted all content.

The example below shows that 3 people have exhausted nurture content for the last 4 casts, i.e., these people are not receiving any content for the past 4 nurture casts.

Similarly, the bars on the left of "0" on the x axis shows the # of people that'll have their nurture content exhausted in next 1, 2, 3, … casts. People who are “exhausted” will not receive any nurture content in the next cast. Hope this helps to clear away some clouds for you around this widget.