> If it's a link to a new domain, it will automatically build a new circuit, and if it's a domain you've already visited, the site will know it's still you, regardless of what circuit you're using. What's the point?

I think you are referring to the fact (yes?) that "new identity" should wipe any cookies stored in Tor Browser data directories, but "new circuit" will not, potentially enabling bad actors to track you to a new domain. But unless you did something foolish (like logging into a social media account registered under your real name or mixing Tor Browser surfing with another browser), that's still a long way from "knowing it's you" in the sense of knowing your exact real life identity.

If I missed your point, please explain.