Maybe it’s a usecase thing. Maybe you grow into it as result of using Discourse as docs early on, but in my area (technical/user documentation) i’d need manual indexing anyhow.
I’ve found that for the maintainer it’s very easy to search and find posts.
But from a user POV which is unknown with your product or new in the topic, they might not know what to search for, in this case structuring makes a lot of sense (in my experience) or users get lost in the maze of docs. You can test this yourself, think of 5 to 10 random docs within various tags you somewhat expect your users to read. Then try to find them by just clicking on your site, if you have trouble finding them yourself, you can imagine how user experience would be.