Differences between Project Manager and Scrum Master?

I often get asked this question, "What is the difference between a #ProjectManager and #ScrumMaster?"

If I were a purist, I would have said Project Managers are used in traditional #Waterfall projects, and SM are used in #Agile projects using the #Scrum #framework. And unlike the PM who is responsible for the project outcome, SM is only a facilitator and a coach. Because the #Productowner (#PO) is responsible for the project outcome.

However, as I come from a consulting background, in my world, I still hold my SM accountable for the project delivery as product owners, in most instances, come from the client organization.

Even though in principle, Agile teams are expected to be self-managing, in my experience, there is still a lot of coordination work that is required from a scrum master to ensure stories are properly groomed, elaborated, sized, and prioritized. If left for PO, we will experience scope creep, production delays, and cost overrun.  

Additionally, client management is still expecting formal status reports. Whether you measure #CPI and #SPI or #Velocity and #Burndowns, you need to present these data points and projections, which again falls in SM’s set of responsibilities.

Lastly, in my experience, the client leadership still holds my SM responsible for the quality of the #product and NOT their Product Owners.

Please share your thoughts and experience on this topic.