I was just in an hour long meeting where I was a bit unclear on what the organizer wanted to get out of the meeting until 20 minutes in. While many people consider this an unsuccessful meeting because they eventually figured out what was going on and thus, boredom had a chance to enter their brains, I consider this a less than successful meeting because I kinda should have had a better idea going in what we were talking about and what the organizer wanted. In this way I could avoid meetings that don't concern me (or which I don't want to be concerned with) and actually be (gasp) prepared for meetings I should actually go to.
A brief aside: I 'prepare' for meetings by reading the agenda somewhere between 2 and 5 minutes before (sometimes I read it on my laptop while we're waiting for the rest of the meeting participants to show); if I am presenting, I usually schedule a half hour before the meeting to get my act together, which usually involves at least one Dilbert cartoon. Life is busy. Meetings are boring. But they are useful, and knowing what is going on is always useful, whether you need to know if you need to fake a kidney stone to escape a dull meeting or if you need to know the fastest route out in case of fire.
Some people are very militant about meetings: they write an agenda in the invite, they write the agenda on the board; they go over every agenda item with the people who attend the meeting, and then cover action items before the meeting closes. And even in these kinds of meetings you can go in and have very little idea of what is actually trying to be accomplished as opposed to what you were hoping would be when you arrived.
The only time I think that being vague about the meeting contents is when you are doing so deliberately. I call this the Switch and Bait; use a vaguely worded or similarly sounding meeting content to attract people who would otherwise not show up. You know, like that exec who has accepted your last three specific meetings and then just not shown up and failed to answer any of your emails. That guy will come to this, because, maybe you've used some keywords to make him think its his pet project you are talking about. Once the squirrelly people show up, you tell them that you will be talking about X, but only after you've talked about what you REALLY need to talk about, usually with a very thin connection between the two. Traditionally people then spit out what you need about X so they can get to Y. Effective on occasion, Switch and Bait is not a good meeting habit to get into--use it sparingly or people will just stop showing up to ALL your meetings.
However you wish to communicate it (agenda items, goals, talking in person), before the meeting I like to be clear about why we're going in and what I want to come out of it. For example, I might set up a meeting with the lines"We're losing data when we move content to production; I'd like to find out possible reasons for that and come up with at least two ways to mitigate it." Everyone knows what the meeting is about. They can come "prepared" or not (some people are VERY eager to weigh in on things and will appreciate the time to do their homework). It also gives a clear indication of how to stick to the topic and when to determine the meeting is over.
For example, someone who comes to your meeting to complain about the content loss can be redirected to the meeting purpose, which is to figure out how it happened and how to prevent it happening again, not to blame anyone or further vent on the topic ("vent" was originally going to be "piss and moan" but I am a lady). Once we have at least two ideas, if people want to stay and give more, great; if not, you can end the meeting...even if it didn't go the full amount of time. Yes, Virginia, Meetings Can End Early.
I'm a big fan of using early meeting endings as incentive to work the problem presented in the meeting; for example "Guys, if we can just find one more mitigation, we can all get 25 minutes of our lives back." Most people love that idea.
Ok. Speaking of meetings, I need to "prep" for my next one. What does the world of Dilbert have to offer me today? God bless you, Scott Adams.