Let's say you have some Sales data and you're displaying the Sales for each weekday in the previous week. By doing this with the Superstore data set I get the below chart. See anything wrong with it?
Yep. There's no Monday in this.
How do we solve this? Easy.
Go to 'Analysis' at the top of Tableau, then 'Table Layout', and then (in this case) 'Show Empty Rows'.
Ta-da! Monday has appeared. Now it's clear to the user that Monday was a stinker for sales.
Another example where you'd want to use this feature might be in survey data. If you have a Count of the Responses for each Score from 0-10, you might find that you have some Scores without any Responses. If you exclude these values then it may be misleading for the user.