It is called comparative advantage – even if the micromanager actually is better at their subordinate's job, their added value is usually much higher when they are doing their own work. They should not lose time by doing work which they are not responsible for. It is simply more effective when a skilled CEO devotes all his time to running the company and doesn't do operational work or bookkeeping, even if he could do these things better than the people whose job it is.
2. Opportunities are costly
This is interconnected with principle number 1. The costs of opportunity are present when we are involved in less lucrative opportunities than we could be, and when we don’t engage in the activity that has more worth. Therefore a manager should not open all his e-mails and answer all the phones, because it is often more beneficial for the company when the typing and answering is done by his subordinates.
3. Unclear responsibility
Micromanagers have the inclination to take credit for their subordinates' successes, but they take no blame for failures. This is a violation of the management rule that authority and responsibility must always remain together. Managers should delegate both responsibility and authority, because only then can the worker decide how to accomplish the task – and legitimately face the possible consequences of failure.