Simulating a user-interface is typical design strategy in a user training demo software. Certainly, the first-time user would benefit greatly from this type of visual simulation approach in the initial stage of learning. That is particularly so in gaining proficiency with functionality of each user-interface component of a software system as large as Mathematica.
Example1: Gram-Schmidt process package
Simulating the look and feel of a Mathematica notebook illustrates clearly the functional relationship between the Mathematica command and the corresponding visualization with a saving of thousands of words.
Example 2-1: Converting numeric data to picture
Mathematica allows interactively the conversion from numeric data to picture, and vice versa. For instance, there is an example in the Mathematica Book of manipulating image processing, but not the data for it. This little animation visually explain how to use Mathematica user-interface to construct numeric data out of a picture while the text version would easily become confusing and misleading.
Example 2-2: Processing image using SVD
Once the picture is obtained, using Mathematica to do image processing is a breeze. Here, explaining the Mathematica procedure to accomplish a given task can take a different outlook from the actual Mathematica user-interface for the sake of better communication.