A good PM can also make sure a team gets resources they need, that workloads are achievable, that there's enough slack for emergencies, and pick up on bottlenecks and frustrations before they happen. Since I'm shit at organising I insist on my team having at least a de facto Project Manager as part of my continuing philosophy that the best manager works as little as possible, because if you have to manage something something has gone wrong.

All of this assumes there's a functioning company behind them, though.