The Zettelkasten has spread widely as a tool for writing, on the strength of Niklas Luhmann's prolific output — accompanied by the narrative that starting from notes is far easier than starting from a blank page.
But surely not everyone who uses a Zettelkasten cares about writing. Is it fine to use a Zettelkasten even if you don't write? Setting writing aside, the benefits you get from a Zettelkasten are
- knowledge management
- insight generation
- writing practice
these.
I think those benefits alone are motivation enough to keep a Zettelkasten going. In fact, even if you never write, I'd say there's effectively no other framework that can take in your thoughts as broadly and bottom-up as the Zettelkasten does.
Still, since you've decided to give the Zettelkasten a try anyway, why not start writing too? Rather than grinding away at writing a book, try something light — microblogging somewhere like Twitter. One of my favorite sayings is, "If you don't know, learn; if you do know, share." I think it's good to share the knowledge you pick up while managing knowledge through your Zettelkasten.