This allows clients to essentially go out and find the relays where an npubs notes are located so you don't have to technically have a relay in common. This enables relays to be decentralized and clients to do the legwork to find the content based on the relays attached to the nprofile.
At least that's how I see it. I could be slightly incorrect in my understanding here nostr:npub1l2vyh47mk2p0qlsku7hg0vn29faehy9hy34ygaclpn66ukqp3afqutajft nostr:npub1v0lxxxxutpvrelsksy8cdhgfux9l6a42hsj2qzquu2zk7vc9qnkszrqj49 are experts on this topic and can help correct me.