In my experience, the main disadvantage to developers writing documentation is the potential for poor writing. The main disadvantage to a dedicated technical wr

In my experience, the main disadvantage to developers writing documentation is the potential for poor writing. The main disadvantage to a dedicated technical writer authoring documentation is inadequate understanding of the software, including what it does and why. Some developers enjoy writing, and would do well at writing documentation for their own software. I suspect at least most developers could be good writers if they practiced at it, but if writing is a task they are being forced to do against their will and desires, that will likely reflect in the writing. If nobody on the project enjoys writing and does it well, then it may be worth bringing in (at least part-time, or on a per-project basis) a dedicated technical writer. But at least one of the developers should be prepared to explain things to and answer questions of the technical writer.