A promised advantage of the Zettelkasten system (and, I think, shared by any other form of Associative note-taking systems) is that by virtue of being bottom-up and allowing structure to emerge primarily by the links between concepts, it allows for interesting topics and questions to be surfaced to the user, rather than the traditional top-down method of “trying to come up with an interesting thought or question, and then taking notes on prior literature about it”.
This is explicitly called out by Ahrens in How to Take Smart Notes in the section titled “Nobody Ever Starts From Scratch”.
Much of the prior art on associative note-taking systems (at least, that I have so far encountered) is centered around non-fiction writing and academic use. I don’t see any reason this advantage should be limited specifically to writing, though, as it seems just as likely that notes will cluster around an interesting opportunity for a software product, for instance.