A good PM is invaluable. They are a multiplier. They work with you, and remove distractions and bottlenecks before they happen. You can absolutely see them pulling their weight.
A bad PM can be a disaster. Teams attached to the project will be out of sync, and everyone will be CYAing because the PM will be blaming everyone but themselves when you discover (too late) that something was missed.
Having worked with both, I'd much rather have no PM than a bad PM.