Why do we come up with our best ideas in the shower, or during a walk? These Eureka! or Aha! moments are the results of our unconscious minds making the creative breakthroughs that don't come during hard mental work. They come as a result of hard mental preparation.
While we still understand very little about the creative processes of the brain, this fundamental insight, that it is productive to allow the mind to wander, can inform the way we decide to cultivate habits of mind and evaluate decision-making processes like group think.