Mine is for consolidation of knowledge. For instance, when I study math and I write a pen and paper proof as an exercise I then write a clean note from scratch and link to other theorems or corollary notes I have etc. Similar stuff for computer science or programming. I find out that this process solidifies the work I'd already done and make it less likely to forget.
I also think people get a bit too dogmatic about the ways to use technology to help improve your life. Like, what the heck complex rules about Zettelkasten? I don't know what kind of expectations they have going into this. Do these "influencers" telling you how to use it sell the promise of the ultra-intelligent god from the popular meme? Just open the damn editor and write, you will find what works for you through tinkering and iteration.