If the project has a fixed set of tasks to be completed, select this option. This will then produce a warning if you try to add additional tasks to the project.
Select this option if the project is not billable. This information will be used in time log reports in order to indicate that the hours logged to the project are not expected to be billable.
Select this option if the project is not expected to contain its own tasks, but rather references to existing tasks located in other projects.
Use cases for virtual projects are sprint backlogs or other types of work lists expected to represent a list of priorities across the primary team and project location of the tasks.