WSJ writes that brainstorming may work better if done individually:
Teams aren’t necessarily so great. “There are so many things people do in management because they think it’s good, but there’s no evidence for it,” says Paul B. Paulus, a professor of psychology at the University of Texas at Arlington. “Teamwork is one example. Brainstorming is another.” Prof. Paulus conducted research on the number and quality of ideas of four people brainstorming together versus four people brainstorming by themselves. Typically, group brainstormers perform at about half the level they would if they brainstormed alone.
That’s why if you don’t carefully follow procedures, you risk wasting a lot of energy. “If you leave groups to their own devices, they’re going to do a very miserable job,” says Prof. Paulus. But if people brainstorm alone after the group brainstorming session, it can be productive, he says, adding, “It’s ironic: You tap the benefits of groups alone. Everyone still presumes the best brainstorming is group brainstorming.”