I have always relied on prototyping and have written many posts on that subject. However prototyping is not just about efficiency or cost savings. It is also about experimentation. Prototyping tools enable product managers to experiment with things directly and apply their thoughts to a tangible deliverable, without having to rely on another person.
No matter how senior a product manager becomes, he or she should not lose the ability and the urge to prototype. To prototype is to experiment. To experiment is to get feedback. To get feedback is to improve. To improve is to succeed.
If you think you are too senior to prototype, consider this. @guptathink, Vice President of Product Management at Groupon builds prototypes with @Axurerp. I heard it directly from him.