"They're freaking out because no one has gotten an agenda... this definitely isn't going to be a meeting as usual."
--Our client, about his attendees.
We frequently don't publish a detailed agenda in any of the event materials given to the attendees. If we do, it ends up being no more detailed than a start time and rough break/lunch times (and perhaps a rough end time).
Not having an agenda does several things:
It allows attendees to fully engage. Though it drives "Type-A" personalities a little nuts, not having an agenda allows attendees to give up control (of their time, not their responsibility/accountability), relax, and go with the event. They want to see what's next.
It takes away pre-conceived notions. If an attendee knows that finance is going to present at 11, they have all morning to think about how unengaging that presentation is going to be. (Whether or not it actually IS.) They focus on the content of the moment and it gives the presenters an opportunity to frame the conversation how THEY want.
It prevents ducking out. "Well, it's only marketing, surely I can duck out and take care of XYZ..." If you don't know what's next, you don't know if what you're going to miss might be vitally important. At a previous event, attendees wanted agendas so they could schedule time with their families (some had come along for a post-event vacation) during the general session. Good for the family? Sure. Good for the content? No.
It inhibits clock-watching. Presenters finish early or, more often, run over time. Not having an agenda gets rid of the toe-tapping, "He's 3 minutes-and-counting over his allotted time," "When will she be DONE already," sentiments out in the audience--decreasing impatience and increasing attention. Likewise, if a presenter goes "short", the audience isn't left wondering why they didn't take up their full 40 minutes.
It allows for on-the-fly changes. During the middle of an event, we sometimes need to switch a presenter or change the direction of the content based on what is happening in real time. Without published agendas, we're able to do this seamlessly--and the audience is none-the-wiser. Do they know that Presenter X failed to prepare and so we had to substitute Presenter Y? Nope. Do they know that because XYZ happened earlier, we chose to invite the keynote speaker from yesterday back? Nope. Do they know that we're throwing in extra activities because the energy seems low? Nope. They're going with the flow, and we're able to better do our jobs.
Not publishing an agenda may not work for all events--and often a minimal level of detail (when people go to breakouts, when the day begins, etc.) is needed in written form. But when one has the option, don't have a minute-by-minute breakdown of the event available to the public audience.