One of the main things that I take into account is the intended audience. If there are strict Can Read User Criteria being put in place then I don't see an issue with a new knowledge base being created (also taking into account the volume of articles that will eventually reside there).

If the intended audience is more of a 'global' or open to a large part of the organization, then the content should be house in a 'public' or Self Serve Knowledge Base.

We currently have more than 40 Knowledge Bases but over 90% of the company would see only 2 or 3 knowledge bases at most. Majority of them are specific to internal teams/processes.