If you have a large production environment, you can simplify the configuration and management of your system by designing your project as a collection of smaller "included" projects.
Included projects can operate independently, however, they share resources and operate interdependently during runtime. This means you can create and test projects representing functional or physical sections of a plant, and then gradually bring them online. Ongoing maintenance can then be managed with a minimal impact on production.
For more information, refer to Including projects.