As the whole purpose of an API is to connect heterogeneous clients with the same backend code, it's inevitable that APIs should be as independent as possible and as loosely coupled as possible with the calling clients.

In a loosely coupled design, APIs are independent, and modifications in one won't impact the operation of consumers. Within an API, the components get added, modified, or replaced. However, the loose coupling approach offers clients better flexibility and reusability of APIs while its elements are added, replaced, or changed.

Having a loosely coupled architecture in REST API server designs facilitates the client and server as both follow and respect common semantics. If the API modifies the meaning of its response, then the client needs to be aware of it and act on those new responses accordingly.

Well-designed APIs exhibit loose coupling and well-composed functionalities across service boundaries to maximize scalability factors.