Substatuses are included in the ServiceTrack > Projects > Open Projects and Closed Projects list views, which can be filtered to make it easier to find particular projects of the same substatus. The substatus colours also make it easier to know how you're tracking with the overall status of projects.
In View Project
When viewing a project, the overall substatus will be shown on the project header:
From the Project Progress tab
Substatuses can also be seen in the Progress tab of a Project:
When viewing a project, click Edit Project towards the top right.
Editing the overall substatus
From the Project Detail on the left, you can edit the project's overall substatus: