Scheduling meetings and aiding in calendar management for everyone. Running meetings and taking notes. Collecting and assembling agenda items in advance for any and all meetings. Setting up and handling logistics for team events. Managing team-related documentation on the company wiki so it's always up-to-date. Helping schedule any phone calls or meetings you need with candidates, partners in industry, customers, etc. Catering food for customer meetings. If someone's going to give a presentation, making sure everything is in order, setting up and running A/V, recording the presentation if desired, etc. Keeping track of annual review, six-month, and quarterly check-in cycles and helping you make sure you're hitting every single checkbox for all of your people. I could keep going but after a certain point many of the duties end up being specific to your team or organization. In general, though, there are probably many things you do that don't necessarily require your specialized expertise and knowledge.
There's some overlap with what PMs do, but generally this person is focused on the team itself instead of specific projects. You might feel that's what you're supposed to do, but once the team is big enough you'll find yourself in a situation where you don't have time for the people on the team anymore -- or at least not as much as you feel like you should.
Offloading this stuff frees you up to focus on people, hiring, retention, unexpected urgent things of a variety of natures, and engineering (maybe not writing code but working with folks to make sure everything that's going on makes sense, meshes together, is aligned with broader objectives, etc.). If you run a larger organization and have managers under you, it frees up your managers to do the same. They'll spend more time with their people and less time on logistics.
