When I was in college I had an excellent CS professor who had chosen as one of his research areas education in computer science. One could argue that it has worked out well for him since he is the department chair and a full professor today.
Going through his classes I learned, which I probably already knew but didn’t realize, that I’m a visual learner. While I read constantly and I understand what I read just fine, if given the option of reading text or looking at graph or diagram I’ll take the latter every single time. It could also mean that I’m lazy but for the sake of argument we’ll ignore that possibility for a moment. (Even if it might actually be true.)
You can see this preference today all over my desk. I have notebooks full of notes and little pictures, books with yellow post-it notes marking pages of diagrams, and a ton of graphic filled design documents that I’ve written sitting on my hard drive. It’s that last one that is really interesting to me because I’ve found that littering a design document with diagrams helps solve two huge problems:
1. Design documents are generally horrifically boring.
2. A lot of times people don’t actually read them.
Now, part of the solution for Item #1 I read about years ago and I think is summed up fantastically already. In short, writing well and being funny encourages people to read.
If, however, that isn’t enough to make reading the words happen then a picture can get the idea across despite the user’s best efforts to ignore it. Let’s take an example.
First using words:
“In order to log on to the Surround SCM GUI client the user will enter their username and password information and click the Connect button. Once the credentials are validated the main client screen will be displayed. If the credentials are invalid then an error message will be displayed that shouldn’t mock them for being forgetful.”
Now using a picture made with the fantasic OmniGraffle:

Both get the same idea across but which one has the lower barrier to cross for the attention of the user? Think of it as reading a book versus watching a movie made from the book. The movie (generally) gets the idea across the same but it accomplishes it in two hours while sitting in comfy chair with a box of popcorn. The book, while rewarding, won’t be done in two hours and you have to make the popcorn yourself.
This isn’t the greatest viewpoint to take for everyday life, picking a movie over a book, but I think it is a very good one when it comes to software design. If by making the design so easy to digest for the reader, especially those in areas like sales and support that have better things to be doing, you can get much better feedback much earlier in the process.
(And that’s a good thing.)