In a scenario, where we are looking for communication which is not synchronous and reliability is of most important, Azure service Bus is good candidate.
In an asynchronous scenario where the consumer system takes some time to process, having the messages stored is important.
In a scenario where there is requirement of Enterprise level features (see question 7).
Where there is need to decouple applications of any size hosted natively on Azure, on-premise, or from any other cloud vendor.
