3 ideas
A manager's output is defined as the output of the organisation they run plus the output of neighbouring organisations under their influence, not their personal activity. It follows that a manager should be judged by team results, and should spend their time on whatever activities most raise those results.
Every managerial activity has leverage, meaning how much it changes the output of the organisation. Activities are high-leverage when one action affects many people (such as a key decision or setting a standard), when it affects someone's output over a long period (such as training or a performance review), or when it supplies a crucial piece of knowledge at the right moment. Managers raise output by trading low-leverage tasks for high-leverage ones and by delegating wherever possible.
There is no single best management style. The right style depends on a subordinate's task-relevant maturity, which is their experience and competence on the specific task in front of them. For low maturity the manager gives structured, close direction. For medium maturity the manager shifts to two-way support and communication, and for high maturity the manager sets objectives and monitors lightly. Because maturity is tied to the task, the same person may need close supervision on a new assignment and autonomy on a familiar one.