It provides as much security as you have trust in the people you share it with. If I set one of my documents to "anyone with the link" just so that I can access it when I'm not logged in, and I'm careful to not share the link with anyone else, then I'd argue that it's still provides some security because I trust myself.
If I shared a document with only you (directly, not using the "anyone with the link" permission), I couldn't stop you from taking a screenshot and sending that to whomever you pleased (or printing them out and leaving them in a conference room, like you suggested). Sharing documents online in general can be troubling if you don't trust the people you send them to. It's easier to share a link than share a screenshot, though, and a link would provide continued access going forward, and could remove deniability that the screenshot was faked.