One thing, possibly less significant than many of the other suggestions here, is the difficulty in improving. If documentation is not done well and thoroughly from the beginning, it makes it difficult to improve later. Rationale and successful improvements cannot be made as easily when new employees cannot understand the reason for the previous work. I have run into problems like this in my work where I want to make a change to reduce some of the burden off of the process only to find the company moved to the thing I am changing but without enough rational.

Additionally, sometimes documentation was required but it is so difficult to change, it makes employees not want to make changes so they avoid it at the expense of the product or people making it- for example extra checking and documentation steps due to poor quality at the end o the process instead of fixing the issues at the source.