I believe that this refers to if the view is empty that you are subscribing, then the email will not be generated and sent. It may be based on # of records = 0.
So, the feature itself is an early form of data-driven alerting. Jonathan Drummey wrote a blog post about this feature:
The "Task in your workflow" verbiage isn't referring to any "workflow" feature that has been added to Tableau Server. It's just a use case example that is referring to your ability to set up conditional emails should you have access to data from a hypothetical workflow system. So let's say that you want an email when you get a new task assigned to you, but your workflow system doesn't support that functionality. If you have access to the data, point Tableau at it, filter the data to your own tasks, then set up a Relative Date filter that looks for the newest of your Tasks. Schedule your subscription for an Hourly schedule (or faster if necessary), and you'll get an email when the task comes in.
Thanks! Exactly what I was looking for.