The value delivered by program reviews critically dependent on the quality and completeness of the information provided.
Individual projects provide information about their world: progress, milestones, risks. Integrating that information across a set of projects, and understanding where to focus attention can be difficult. Often the program or portfolio manager is dependent on a key person being ‘in the room’ to provide a perspective, or to address or highlight a pattern that only emerges after several projects have reported.
It’s possible of course, that because an issue is being addressed at a lower level in the projects, then it never reaches the review. Portfolio Manager can help to surface issues that may otherwise be missed.