You need a breakCheck out the article in full to see his exposition and explanations.
You need to share
You need some sympathy
You are called to equip
I'd like to add a few more reasons why pastors should be sharing their pulpit as part of the cultivation of elders/leaders.
1. If you don't, you're complicit in wasting other men's preaching/teaching gifts. (This ties into Larson's point on equipping.)
2. It is unhealthy for a church to become dependent on one man/voice.
Your church needs to know that it is the Bible properly taught that is their source of strength, not a particular man and only that man teaching it. This is the inner error in many video venue enterprises. Some will say the satellite would not be viable without the "celebrity" preacher preaching, in which case I think it could be argued that if it could not survive without a particular person's voice, it is not viable to begin with. (What happens if that pastor has a heart attack? Does every satellite shut down? Or do they just play old videos?) At my church, I want to share the pulpit so that the body benefits from multiple voices among us and so they do not get to equating worship with my voice.
3. You need to sit under gospel-centered preaching and receive.
This is something I really need to work on. At the moment, I give up my pulpit several times a year -- which is good -- but it is typically when I'm guest speaking in someone else's church. But I need to sit under preaching myself. I need to let other capable men preach in my pulpit while I'm in the congregation, worshiping under the word proclaimed.