It's not a joke, BGP servers used to authenticate each other with this in the late 90s. This was also before NAT was really a thing.
Or in the case of a PNI between two ISPs over their own cross connect, you absolutely want to have a mutual level of trust and cooperation between the BGP peers on both sides of the session.
And then other more modern methods of verifying that the IP blocks you're seeing from some other AS are legit, like verifying their RPKI signatures, IRR entries, etc.
I mean it's the only auth that exists for BGP, so why would you not want it?