I don’t know. :)
But I think it’s used when you want to connect a vCloud Air network (which is part of a Disaster Recovery or Virtual Private Cloud setup) with the network of a vCloud Air PaaS such as vCloud Air SQL. I base this on this vCloud Air SQL Users Guide that talks as about enabling the service network to connect a vDC (vCloud Air Virtual Datacenter) to the vCloud Air SQL network.
Will add more to this post if & when I get to know more.