I have worked in private company and I have also worked in public company. I found that documentation is important for all networks. Without a detailed network diagram, it is so hard for trouble-shooting. Not to mention to maintain it, just to make myself to understand the networks may take up a whole week (depends on the network size). One thing I have learnt from different jobs, the more documentation about the network, the easier and quicker for me to get my job done.
Not only a detailed network diagram is needed, a rack layout diagram should be part of the documentation. I have been in a satuation openning a rack with full of equipment on a 42RU rack. I have to go through the label on each device one by one to find out the right equipment for me to work on. If there is a nice rack layout diagram, I can have a good picture of how the rack look like and save a lot time of finding the right device.
I think being a great engineer, not only good technical knowledge is needed but also a excellent documentation skill to provide good information for other engineer to work on your work.