Groups contain a valuable mix of perspectives and a range of problem solving styles. The individuals in the group bring their own unique knowledge/skills/experiences and combine with the others to provide a vast collective pool of knowledge. Within this pool are all potential elements of a creative idea. An idea is a new combination of existing elements. Once shared new elements reside, however fleetingly, in the minds of those listening. A new element can be the missing ingredient or needed spark that stimulates the new idea. However, whilst the new idea may never have happened if another person hadn't added that vital element the new idea can only ever be formed in one person's mind.
You can only combine/synthesize/associate two things you are aware of. The benefit of working in groups is in their ability to stimulate new ideas in individuals. The final act of creativity has to be an individual one.
Would love to hear anyone's thoughts on this.