I've been thinking about this a fair bit. Consider the following scenario -
You have a mature product development team, that's cross-functional and has everything they need to build and ship. They've been working together as a team for a long time, know the technology and product inside and out. They dont have 'big company' impediments like excessive governance and reporting. They're co-located with product management, sales and support and have solid clarity from their product manager and have supportive management. They deliver every 2 weeks at a sustainable rate and there's little to get in their way.
Does this team need a dedicated scrum master? If so, what value are they adding?