By definition, integration involves wiring together multiple systems

Developing integrations is most safely done againt lower versions of these systems; QA, Sandbox, Test etc.

Once an integration is developed, it becomes valuable when it is deployed to production. This may involve changing multiple configuration elements such as URLs and credentials, but also making different structural choices; emails may be generated but not sent, QA versions may be against different API versions than production (in the case of testing an upgrade candidate, for instance).

Flow handles this by means of Environments, which are effectively overlays to a functional structure. Like a transparent page in a book, they obscure some parts of the structure and leave others to show through.