Following my new found interest in Neuro Linguistic Programming (NLP) I read an article on frames. In NLP frames is used to provide a context, focus or guidance for thoughts and actions. One type of frames is the outcome frame. An outcome frame provides focus on what you want to achieve, the achieved affects and the resources needed to achieve it. This line of thinking can be applied to the subject of meetings without agendas.
In some of the companies I have worked in or work with, people are meeting happy (compare with trigger happy). Not a day pass by without me being called into several meetings. People say we need to have a meeting about this or that. The meetings lacks an outcome and are rarely timeboxed and when the people exits the meetings, they are often confused as to what was decided and what is expected from them. I do find that people still often feel satisfied, while I always feel frustrated.
The reason for this, is that the outcome was to have a meeting, which was achieved. However, with a clear goal, a good agenda and a timebox you set the wanted outcome and this gives you a context for making decisions and assesing your behaviour.
So make it a rule for you to say no to meetings without a defined outcome. There is no rule without exceptions, but remember the downside of having meetings without a defined outcome.