Scrum Master
The person whose job is to remove blockers, protect the team from interruptions, and keep the process working, not to manage people or assign work.
A Scrum Master has one real job: make the team more effective by getting things out of its way. That means removing blockers, shielding the team from mid-sprint interruptions, facilitating the standups and retros so they are useful instead of theatre, and coaching the team on how to actually work, not just recite the ceremonies. They are a servant to the team, not a boss over it. They do not assign work, they do not own the backlog, and they do not do performance reviews.
The role gets misunderstood in two directions. Some treat it as a glorified meeting scheduler who reads the standup script. Others quietly turn it into a project manager who pushes the team to commit to dates. Both miss the point. The value is in spotting what is slowing the team down, often something organisational and uncomfortable, and having the standing to fix it. A Scrum Master who only runs meetings is overhead.
Here is the honest take: small teams rarely need a full-time Scrum Master. A team of four or five engineers can run its own ceremonies, and the facilitation work is a few hours a week that a tech lead or senior engineer can absorb. A dedicated full-time Scrum Master earns the seat when you are coordinating multiple teams, when the organisation around the team is the main source of blockers, or when a team genuinely cannot self-organise yet. Below that, the title is a cost looking for a justification.
We have seen plenty of teams happier and faster after dropping the full-time Scrum Master and folding the work into the team. We have also seen teams drown because nobody owned the blockers. The role is real, the full-time version is often not.