Change Management - Internal and External Change Agents (A-plus Writer)

With respect to change agents, should organizations use internal or external change agents? Why or why not? Can you see any advantages or disadvantages of either approach?

Details:

This is a threaded discussion answer should be in paragraph format (6-8 sentences and no more than 2 paragraphs)  and 

American Psychological Association should be followed

I need this returned to me by 11:00 PM EST 10/06/2013