Azure Service Bus is available in three tiers - Basic, Standard, and Premium. The Basic tier provides only very basic queuing, whereas the Standard tier provides many more features such as topics, transactions, de-duplication, sessions and forwardTo/SendVia. The Premium tier is based on the existing Standard tier but with the added enhancements consisting of isolated CPU and memory resources. This isolation from other tenants provides scalability, greater predictability, performance, and a larger message payload.
Normally, you would use the Premium tier for systems that are latency sensitive; if you are receiving server busy errors from Azure, you need to scale your systems on a massive scale and you will send more than 3000 messages to a topic per second.
Pricing for the Premium tier is priced at a daily flat rate per the messaging unit purchased. There are no other charges included.