Sub-systems are a powerful feature in Digital Twin models that allow you to "break down" or categorize your model in the way that best suits your company's needs. These are added by Advanced content creators inside the frontline 3D Studio SDK.
To activate a sub-system, simply click on it in the left panel and the right panel will open with a list of the Digital Twin's sub-systems. You can activate a sub-system by pressing the power button near its title. It's easy to skip between sub-systems as needed.
It's important to note that a sub-system doesn't have to be defined as a specific part or parts of the Digital Twin model. It can even be defined as a certain state that the Digital Twin should be in, such as being x-rayed or with animation turned on.
So if you want to customize your digital twin model to fit your company's needs,
sub-systems are definitely the way to go.