These tools: Wireframes, process flows, functional specs, UML documents; They were invented to solve problems, not create new ones. Sometimes simpler methods of communication need to be invented to simplify the message.
Most large web sites are built cumulatively one section at a time. The web enables this kind of ad-hoc building and it's both beneficial and dangerous when pages and sections can be changed without looking at the whole picture. When web sites are analyzed from the bottom-up and top-down skeletons come out of the closet.
After the process of reduction and pattern-matching, a simple diagram like the one above can help people understand a model without having to dig deep.
Diagramatic Design can be used to literally get everyone on the same page. If you look the parts of the process of development through the eyes of the people who are going to use the product, everyone will contribute to the customer's experience because it's the only experience worth building for.
The challenge with complicated rules is that eventually something will go wrong. Computers are pretty good at keeping the rules straight. Sometimes the process needs the development of a good set of algorithms paced at the right rhythm to make that journey feel right.