I have been talking about the importance of having a PM and a BA on a project for 10 years. Although I still would prefer this arrangement I recognize that few teams have the luxury of pure roles. So everyone needs to have a basic knowledge of project management and business analysis. Even if you have clear roles, it helps when you understand something about what your co-worker is doing. This multi-disciplinary approach really helps if you are moving to a more agile style work also.