The Zettelkasten spread widely as a tool for writing, thanks to the prolific output of Niklas Luhmann. The accompanying narrative was that starting to write from notes is far easier than starting from a blank page.
But not everyone who uses a Zettelkasten is interested in writing. Is it okay to use one without writing? Setting writing aside, the benefits you get from a Zettelkasten are
- Knowledge management
- Generating insights
- Writing practice
I think these benefits alone are reason enough to keep a Zettelkasten. In fact, even if you never write, I don't think there is any other framework that can take in thoughts as broadly and from the bottom up the way a Zettelkasten can.
Still, since you've decided to try a Zettelkasten anyway, why not start writing too? I don't mean grinding away at a book. I mean something light, like micro-blogging on a platform such as Twitter. One of my favorite sayings is "If you don't know, learn; if you know, share." I think it's good to share the knowledge you pick up while managing what you know with a Zettelkasten.