You can create demos of any software application or Web page interaction or administrative task. It's the quickest way to show some software feature or nifty technique.
I find it slightly easier than writing out all the information, but much more compelling -- taking less effort to view than to read a lengthy explanation.
I use Camtasia Studio to capture animated demos of me showing features of an application.
I didn't understand the value of using video showing the narrator, until I saw a promotional video on TechSmith's web site:http://www.techsmith.com/videos/studio/CS3/overview/cs_home.html