Brainstorming - a group problem-solving technique in which members spontaneously share ideas and solutions.
Notice that the definition doesn't use the word critique anywhere in it. That's because brainstorming is meant to be an activity in which all participants, even if it is just one person, are meant to throw out as many ideas as possible without shooting any down under existing premises and allow the organization and planning of those ideas be placed on the back burner.
Sounds like a wonderful way to come up with new ideas and possibilities, eh? It is the day dreaming portion of being a knowledge worker - where you get to think without reality. But that's the part where brainstorming can go awry, if you let it.
Brainstorming must be done in the overall context of a plan or a project. If one is just brainstorming willy-nilly and simply for the sake of brainstorming alone, it is a rather pointless activity that is orthogonal to anything that we as knowledge workers should be focusing on. In fact, if brainstorming is conducted without the results of sessions being used to impact an already existing project or goal then it is, in the best-case of a single person, a huge waste of time and waste of mental energy used to flutter out ideas that most likely will not be used. In the worst case, it can demoralize a whole team if they are coerced in to a highly collaborative activity that sucks up double-digit man hours all to produce nothing if no actionable steps or follow through is executed on the residual items left over from a brainstorming session. One can guarantee this does not happen if brainstorming is put in to the context of an overall plan or project and is used as the basis of forming next steps in a project.
An experience I have had at the professional level involves a brainstorming session close to the initial launch of a highly visible web development/services project I was a part of. Toward the end of that project, when frustrations were high and deadlines were starting to slip, management thought it would be a good idea to have all of the key participants gather in a room and have a brainstorming session on identifying problems in the project and how to correct them. As an exercise in how to conduct a brainstorming session it was executed well. Someone in management had been doing his/her homework on the subject of how to conduct a successful brainstorming session. Lots of ideas and thoughts were shared and displayed wonderfully as sticky notes on a whiteboard - there were literally hundreds of them. Unfortunately, what management did not do was use this brainstorming session in the context of the full project. There were no actionable items created as a result of the session and no follow up meetings were held - contrary to the lip service given by those organized the affair. It was as if hundreds of good ideas and thoughts suddenly cried out in terror and were suddenly silenced. The voices of all who participated were just simply ignored.
This particular session ultimately did more harm than good. To this day, that brainstorming session still gets mentioned in the office in very negative connotations as a useless waste of time and no one today wants to engage in any formal brainstorming sessions out of distrust from the original. This is due to the fact there was no follow-through - the brainstorming was not done in the larger context of a project plan or goal. Had the ideas used in that brainstorming been used for actionable items immediately as part of our project plan, two things might have occurred: 1) the rest of project may have gone much more smoothly (it did not, no problems were addressed) 2) the folks doing the work would have had confidence in brainstorming activities and would have engaged in more.