"Almost every project has it; there's nothing new about Agile Release Planning." Not quite! What's different about Agile Release Planning, like many other good Agile practice is that it is lightweight, inclusive, and a living plan that is well socialized. Every release plan is different. The anathema of the traditional release plans, though, are their elitist origins, seclusionary existence, and staleness. The realities of project kick in and then an eerily familiar yet enigmatic (to me) behavioral (anti)patterns start to fortify; the unrealistic to begin with plans morph into contracts between IT and Business and nothing ever changes - budget is set, schedule does not move, and scope of course only increases.
Someone once said to me, "You Agilists are lucky". I think, he meant to say that Agilists are pragmatic and call out the fashionable insanity of planning. The notion that neither scope nor schedule and budget move is untenable. Release Plans are and should be evolutionary by nature. This evolution stems from other Agile practices like prioritization and iterative design practices.
The slide deck below is an aide I use to convey the above message.