Responsiveness is one of the most important parameters for the success of any web application. And asynchronous processing is The Solution for attaining this responsiveness. A server request from the browser should return immediately — without wait for completion. The data flow should be designed in a way that it does not depend upon an immediate response from the server.
There are several architecture patterns to do this. But a major problem with asynchronous processing is error handling. How would the client know if the request failed? We should not lose data in the process. In fact, a fire and forget service, cannot afford to fail. Even if the processing failed for some reason, the data has to reach the DB.