Using technical writers who are familiar with the product can improve design, functionality and usability. Developers can identify defects and often may know at least one solution. Working with technical writers, developers and add features, improve current features and fast track design.
Often, writers are editors, only taking content and improving layout, not usability. Find a GNU Linux writer who is also a developer and you get a 2fer.
I was once introduced by Rick Moen as a triple threat: Dev, Writer, Law
Sometimes I joke about being a unicorn.
As a technical writer, understanding copyright and trademark is essential. Being able to automate documentation processes for fun is efficient, and improving workflows is effective!