Communication is so important. We’re social creatures and we need to communicate in order to cooperate. The most important part of communication is comprehension. We want our message to be clearly understood. Too many conflicts have started because of misunderstandings.
Communication comes in many forms, but often we limit ourselves to one method and often that method is the written word. Writing has its benefits and can be hugely powerful when wielded properly in the pen (or most likely, the keyboard) of skilled wordsmiths but not only are we not all highly skilled or experienced wordsmiths, but some concepts just don’t translate well through the written word.
In the software development industry diagrams can aid discussion far more clearly than words. A well drawn picture can very quickly bring about consensus in a group. It can also highlight missing elements that only seem to appear when for instance, you map out a process. A drawing of a screen with its components will highlight where there might be user interface issues. A high-level conceptual strategy diagram can motivate and inspire people around a common cause.
But just like any form of communication, a badly drawn diagram can confuse and frustrate. In the same way that words represent concepts and ideas, so do images. Make sure that the images and shapes you’re using mean what you think they mean to the people you’re trying to communicate with. The whole point is to clarify, not confuse.