Adding some practical perspective here since this is a common decision point and the answer really depends on a few things you'll want to nail down first.
The "1 public + many private" model works well when you have a large body of content that's genuinely system-wide — think IT, facilities, HR policies everyone needs — and then department-specific content that only makes sense to that audience. The public KB becomes your front door and the private ones stay scoped. User Criteria handles who sees what on the article level, but having separate KBs gives you cleaner governance boundaries — different owners, different workflows, different review cadences without them stepping on each other.
The "1 KB per department" model mirrors your intranet hierarchy which feels familiar, but it can get unwieldy fast. You end up with a lot of KBs to maintain, duplicate content starts creeping in because nobody knows what's in another department's KB, and if you ever want AI Search or Now Assist surfacing content across the org, fragmentation works against you.
For a hospital system, I'd lean toward a middle path: a small number of KBs organized around audience and governance, not org chart. Something like one for enterprise/system-wide content, one for IT/technology, one for HR/people services, and then evaluate clinical or department-specific ones only if the content truly requires separate ownership and workflow. Keep the number low and use categories + User Criteria to handle the scoping within each KB.
The question to pressure-test any decision: who owns this content, who approves it, and who should be able to find it? If the answers are different enough, that's a KB boundary. If it's just "different department," that's a category.
