Why Engineers Need Good Managers

Someone recently asked me why teams of experienced engineers still benefit from managers. If the team plans the sprints as a group and pulls tasks from the backlog on their own, what is the manager doing?

My opinion is that they don't necessarily need "a manager", but they do benefit from the things a leader traditionally does for the team. I've even been at companies where the traditional "manager" responsibilities were split across different team members. Here are a few examples of how I believe teams benefit from centralized leadership:

Coordination can streamline the integration of parts.
With many engineers working on parts of a bigger project, the final integration of those parts can be very challenging. Small miscommunications can lead to large fixes at the end. By having someone coordinating and aware of the individual parts as they're developed, integration issues can be headed off and this effort can be saved.
Meaningful feedback for growth takes dedicated effort.
While getting feedback from other team members is valuable, they're typically too busy to put deep thought into how you can grow and become a better contributor. Having someone with time carved out for this can lead to much faster growth, and hence the team benefits long term. This also applies to problems the team has as a whole and refining processes.
Communication scales poorly with the number of participants.
It can be wasteful to have the entire team involved in certain communication. Having a dedicated representative of the team deal with a lot of cross-team communication can save the team time internally. Similarly, having them filter company-wide communication can help keep a team focused.
Not everyone wants to do everything.
Different tasks appeal to different people. A leader can keep a team-wide perspective and help balance what needs to get done with what individuals prefer to do. This can end up more fair and efficient than someone volunteering or arguing about unpopular assignments. Another way to phrase this is that they can prioritize what the company needs in situations where it conflicts with individual needs.
Escalation paths streamline communication.
There is a natural power discrepancy between roles at a company. This can make it difficult for individuals to question certain decisions made in areas they're not familiar with. Hence, it is helpful to have a clear escalation route where they can ask questions to someone they're already comfortable with. This can save time and effort across the company, while making sure serious concerns are escalated and addressed.