Many messaging systems allow messages to be automatically acknowledged on the server before they are delivered to their consumers. This feature is useful for transient messaging use cases where it does not matter if some messages are lost on failure (e.g. stock pricing information).
JMS does not currently provide an acknowledgment mode which supports pre-acknowledgment on the server, so there's extra (unnecessary) traffic due to acks having to be sent from client--server.
In reality most JMS implementations provide pre-ack as an extension to the set of JMS ack modes. I would like to propose that pre-ack is added to the list of standard ack modes in JMS.