It was useful when the Internet was small, and all run by nerds who just wanted everything to work. In the mid-90s, the phone number in WHOIS was usually the guy who actually ran the servers. I called people when email auto-responders went awry and caused an email loop, or when ISP's DNS servers had old entries that shadowed web sites we hosted, or when I found a security hole.

Yep, I remember some people in my org having problems emailing a large company. Whois, call number, get tech, get mail guy, gets fixed.

Probably all so they know which direction to point lawyers / government agencies towards when they come knocking about your domain.

They could just send an email to abuse@[domain] like anybody else.

In my experience of recent years, addresses like abuse@, webmaster@, hostmaster@ and postmaster@ normally bounce. It’s a real nuisance when I want to report bugs in web systems, or in email systems where they’re doing enough things badly wrong that they trip (or get close to tripping) spam filters, et cetera.

Sadly I never setup any of those, usually only admin@ and then move on. To be fair I usually list one of the available emails on my sites where it makes sense, or provide some way of contacting me directly. I will definitely create those and forward them to admin@ from now on though. But the issue still remains as others said, now you can claim you never got an email.

... including for ISPs, as I found out recently when trying to report some abuse.

I tried complaining to RIPE but they did nothing.

Which you could ignore, but you can't ignore a lawyer.

Maybe it's better that way, lawyers have to do actual manual work on cases that matters instead of sending random legal threats to every company they can find. Random legal threats are not substitutes for law enforcement.

I can't remember ever being honest when entering WHOIS data, and I own hundreds of domains.

Doesn't that transfer the ownership of the domain to the fake entity/person you've specified?

That assumes the fake entity exists and disputes it.