I don't want to have to hunt for documentation if it breaks. It may have been 30 years and everything but the binary has been lost, and the vendor is out of business. If in that situation all I get is an error code and a link to documentation that doesn't exist, I'd have to start reverse-engineering. And while doing so I'd definitely be cursing the coder who decided that saving a couple hundred bytes of space in a log file in the event of an "abort the program"-severity event was worth dumping this in my lap.
Running such software is asking for a disaster already. At least documentation should still exist, and operational frameworks like ITIL insist on that. It can happen, but is usually telling of an operational culture that disregards maintenance, counting on being able to kick the can down the road as long as possible.
