This diagram is really easy to understand about kinds of coffee and we can see that what they want to say at a glance even though I do not know much about coffee.
source from http://www.lokeshdhakar.com/
This can be an example of good diagram. Using picture and position, this diagram makes it easy to understand the cycle of moon shapes and phases ( which was hard for me to understand lol). If they tried to explain about it not using this diagram but using text, it must be taking more than 2000 words and furthermore, it must be hard to understand.( I guess)