When a person has received every piece of content in a stream, it has exhausted all possibilities and will wait idle until more is added. You can find people that are "exhausted" in several ways.
Member of Engagement Program filter
Create a new smart list, then find and drag in the Member of Engagement Program filter.
Find and select the engagement program in which to find exhausted people.
Under Add Constraint, select Exhausted Content.
Set Exhausted Content to true.
Simply run this smart list to see the list of people that have exhausted all content in the stream they are in.
Go to Marketing Activities.
Select your engagement program and go to the Members tab.
Notice the column called Exhausted Content.
This shows you people that have exhausted all content and those who have not.
You can also see the total people who have exhausted content under the Streams tab on the stream itself.