Whenever possible, we should go for asynchronous communication with clients and other services. Asynchronous communication helps us to decouple code and does not block the calling service. For example, if your frontend UI goes for asynchronous communication with backend services, we make sure the system remains usable while we are loading the required data at the backend. The end user is still able to interact with the system. Even if a service or two are failing, we are making sure other services are returning information and are usable by the end user even if the unresponsive service blocks a couple of threads.

We should use an asynchronous queue or middleware-based communication when an immediate action or response is not required. Say we are logging; we will add the data to queue or broker instead of the service directly.