This pattern will be of use for applications that use messaging to announce events. The announcement of events will involve sending messages to multiple receivers simultaneously. If the message is sent on a publish-subscribe channel, a copy of the message will be sent to each receiver:

A publish-subscribe channel works basically like a broadcast mechanism. It has one input channel which is split into several output channels, one for each subscriber. When an event is published in the channel, a copy of the message is delivered to each of the output channels that are attached to it. Each output channel has only one subscriber attached to it. Each subscriber can consume the message only once. In this way, each subscriber gets a message only once and the message copies disappear from the channel once they are consumed.