You can have zero configuration address discovery in a way that is simpler than IPv4.
You don’t need to worry about what happens when you get to over 200 devices on your local network (not unheard of in at home networks when you start adding IoT devices.
You can have stable addresses across ISPs if you bring your own prefix or use a tunnel.
You save money by not renting IPv4 addresses.
You don’t get as easily blacklisted for email delivery since you dot. Share a /24 with a bunch of spammers.
This is before you get into P2P networking without having to rely on a third party relay.