We've built our internal wiki out in Notion. We use it to store data, collaborate on ideas, organize teams, clients, etc. We are an agency, though, and are often working inside of our clients' tools and systems. Notion can't replace things like Jira for us because to impose change management at that scale on the client side would be a step too far. It has allowed us to much better organize documents, information, and certain files much more cleanly than in Google Drive, Box, or Dropbox (where a lot of this type of stuff used to live).
Because of its flexibility, it's really easy to create a mess unless you get really tight on how you organize pages and content. The delineation between private, shared, and public pages can get a bit messy (mostly because permissions look different between those three types of content, and you can easily find yourself in a situation where you've accidentally shared something you shouldn't, or locked out something everyone needs access to). Like any content hub, the biggest challenge over time is that it can be difficult to find what you need. Search works ok, but can return a lot of useless results if people are using similar words or naming paradigms for their pages.
Notion is highly customizable and incredibly flexible. We've been using it to build out our internal knowledge bases, company wiki, and organize teams and client info. Being able to link relevant pages, databases, etc. has been incredibly useful.