There are usually lots of irrelevant questions in the beginning like "what are we having for lunch" or "why does the statue on LOST only have four toes" but by the end of the process, you end up with a lot of great questions that the group works together to answer.
It is in the answering process that the real idea farming happens. People start to think about how to solve problems, how to change the way things are done and how to create a greater return on their marketing investment. And while not every idea is immediately useful, the process of getting people to develop, consider, debate and approve new ideas is invaluable.
Next time you have a problem to solve, a project to manage or a marketing plan to develop, consider using Question Storming. I think you'll be impressed with the harvest of new ideas.