A. To return responses back on a separate connection in a request and response flow. For example, enabling WS-Addressing to specify a new address to deliver a response.
B. To establish a connection for out-of-band communication with 3rd endpoint. For example, in using WS-Secure Conversation with another business endpoint, a token can be obtained from a 3rd party provider.
C. To tunnel through a firewall and establish a back channel for messages to be sent to a previously un-addressable endpoint. For example, with WS- ReliableMessagingreestablishing a connection through a firewall for acknowledgements.
D. To create a separate connection to an endpoint to gain metadata about an endpoint prior to the initial request. For example, creating a connection to a separate endpoint to retrieve WSPolicy information about how to establish connectivity to a web services endpoint.