https://github.com/nostr-protocol/nips/blob/master/05.md

Can be used as a verifier let's say if you control the domain. But people would need to associate that domain with your real life person.

I mean i can buy pete . red while you own pete . com and copy your Nostr profile.

People would need to know you own .com to identify your account.

So... identifier for easy finding you on Nostr. Easier than the key.