It’s rare that a web service has some intensive processor bound computation to execute. Far more common for business applications, is a web service that executes one or more IO intensive operations. Typically our web service would access a database over the network, read and write files, or maybe call another web service. If we execute these operations synchronously, the thread that processes the web service request will spend most of its time waiting on IO. By executing IO operations asynchronously we can free the thread processing the request to process other requests while waiting for the IO operation to complete.