It verifies that the domain "knows" you somehow and you are somehow associated with it.
And to find people you can say "Follow me on nostr, I'm mike@mikedilger.com" and that works because nip05 contains my pubkey and the relays that I'm at.
Discussion
This can easily be games with typo domains if the target is worth it.
But yeah, helpful when asking to follow.
I didn't realise this. Great I can just share my nip05 ID (iain@cheyne.net) instead of my pubkey.
nostr:note1wgyarpxut54u2g6neazket8867n8d08zdtc4hu5pchndlykvl7aqk0qh24