It's fun to work in a group once in while. Because there are many different people, there are many ideas. In my group we combined many of our ideas into one big/good idea (that was better then any of our individual ideas) that we all liked. It's also helpful to share the responsibility for the project. People have different strengths in skill that they can contribute to the project.
Although this hasn't happened in my group, I could imagine it would be difficult if people disagreed with each others ideas. Also, it would be annoying if people didn't do there part of the project, which fortunately hasn't happened in my group.