Kleppman p. 701:
In log-based message brokers, message retention is independent of consumption; the system just writes to a circular log and deletes the oldest record segments when the disk starts to fill up. Therefore, if a consumer goes offline, it just stops consuming bandwidth. By contrast, in a traditional message broker (AMQP, JMS) setup, a queue with no consumers will take up more and more storage/memory until it reaches some limit or breaks. This makes LBMBs more like batch processing tools; you can just keep running over the same set of messages as often as you like with no side effects.