Scrum Masters need to rock the boat
I once worked with a really good Scrum Master who made my views on the importance of the role do a 180. They can do a lot more then share their screen during the daily, schedule the scrum ceremonies or remind the team to stay in a meeting's timebox.
Scrum Master is the role in which the least damage can be done if it is occupied by an ineffective member (unlike with a bad PO). But it is also the one which can make the biggest impact on a team if overseen by a rockstar.
Teams don't stumble into greatness
Most developers I discuss this with see the Scrum Master as an anchor of stability, a therapist-esque role who makes sure the peace is kept inside the team. In my eyes this interpretation of the role is misguided.
Scrum Masters need to be courageous. They need to be the annoying coach who is constantly in the team's ear. They need to proactively rock the boat constantly, confront and push the team to always improve. They are a leader in the team and have the responsibility to keep raising the bar. A good Scrum Master will proactively push the team out of their comfort zone. It is a red flag if the Scrum Master is only a passive listener and an organizer, only getting messaged by the PO to set up or cancel meetings.
It is said that it is the objective of an Scrum Master to make him- or herself obsolete. That the team has internalized agile values to such a degree that they no longer require the Scrum Master's services. I think this is a picturesque and quaint vision to draw for the role, but it has little place in reality. There are teams who have a larger necessity for a Scrum Master than more mature, well-functioning teams. But the pitfalls team fall into, face and fix are not a binary lever which gets flipped from negative to positive once and stays there. It is a constant dogfight of not letting old habits seep back into the team. A good Scrum Master will never become obsolete.
Influencing upwards as well as downwards
Organizations want to be agile, and they hire Scrum Masters accordingly, but too often does the management not have a real understanding of what agile is: They still want to give their "suggestion" (read: demand) and have their multi-year roadmaps available. Why else are pseudo agile frameworks such as SAFe so popular? It allows the management to retain their influence under the guise of being agile.
What this means is that they possess a unique opportunity to evangelize upwards and carry agile values to the highest levels of the organization or to detect the systematic changes needed to become nimble. Most managers I have contact with have very contrived views on foundational aspects of Scrum, such as the role of the PO/PM or what the intent of working in iterations is. Devoting oneself to these seemingly inconspicuous basics already pays dividends for fostering the right culture.
What a blessing it is to have someone concentrating solely on improving the team. Scrum Masters are spread thin across teams, often embedded in two or more teams. My experience is that this atleast severely hamstrings their effectiveness, if not making their task impossible.