How Important Are Meeting Agendas?

It's been my experience that meeting agendas that feature topics are never as productive as agendas formulated as questions. It's also been my experience that pre-set agendas do not necessarily keep meetings focused, inclusive or productive. Some of the most wasteful meetings I've seen have had detailed agendas with timeframes. 

How productive a meeting becomes has everything to do with the quality of questions used to organize the interactions, thinking and engagement. Actually, I would argue that meetings where people build the agenda as they go in meetings can be far more productive than unilaterally imposed agendas.