Power, control and ICT systems are the most complex part of any asset.
Note how little knowledge is found by visual inspection of these simple examples.
Even wiring cannot always be understood by simple inspection.
You must use drawings. You must search for them without knowing if you will ever find them.
When you deal with wiring and simple devices you now have to find out how the devices work.
Programmable system central parts.
You must find wiring, devices and application code documentation. This will be slow and you will run a substantial risk of error.
When reviewing software you must refer to the running code as any documentation is usually out-of-date.
Network connections are mostly visible but their functioning is impossible to capture in 2D drawings and lists.