You don't really want your senior and staff engineers bogged down with career management, hr disciplinary implementation, team salary budgeting, and all the miscellaneous other duties of a manager. You want them thinking deeply about the code, the business problems, and how the two meet.

In terms of evaluating job performance, you've got peer reviews, deadlines met, contributions in meetings and so forth.

In other words, a manager should have their time filled with other things. Unless the team is really tiny (too many managers), there's plenty for the manager to be doing- planning with product / sales / design teams alone should be enough to keep them busy.