I maintain WAN diagrams and try to update them when any changes occur or review quarterly. The diagrams are posted on an internal IT team resource web page for locations to use as needed for troubleshooting or discussion on network services. The diagrams are also used for audits. I keep a large format print of the diagram on the wall in my office and refer to it regularly when troubleshooting.
At my company we keep a map, and update it regularly, or at the very least a quarterly review.
The maps help us in troubleshooting, but also provide the business customers a good view of how it all ties together, so that asking them for additional $$$ is much easier 🙂