Comparative advantage was first described in an essay on the corn trade. It was to England's advantage to trade various goods with Poland in return for corn, even though it might be possible to produce that corn more cheaply in England than Poland.
The details available at http://en.wikipedia.org/wiki/Comparative_advantage
Micro management is more common than is obvious.
So often you'll see team leads doing the role of engineers, managers doing the work of leads (even engineers), and directors micro managing managers and so on. Maybe (note maybe) they do it better than the people they manage but it doesn't necessarily follow that they much do it just because they do it better (or think that they do it better!)
Setting aside the cliched (though sensible) arguments like - let your team learn from the mistakes etc; it makes business sense for people to to do they own job and leave their team's job to the team - even at the perceived penalty of doing it less efficiently, less quality etc.
Given your limited resources of time and scalability, The law of comparative advantage kicks in. The overall advantage of you doing your job is much higher than you doing the role of someone else who is lower in the food chain. This comparative advantage more than offsets the penalty of your team doing what you would do potentially better, faster, cooler, whatever!
What happens if you can do your staff's role better than they can and if you don't have enough work for yourself? should you?
Unless you are paid very poorly (in which case you should anyway leave your job) you run the risk of not adding enough value to justify your cost and should start looking for a better match between your price and value.