[dsr_]

Suppose you have multiple providers, but one of them screws up and authoritatively denies the existence of all of your hosts?

[bitJericho]

That's what you keep an extremely low ttl for.

[Karunamon]

Which doesn't mean much when a nontrivial amount of ISPs out there don't respect the TTL settings.

Source: Days-long service degradation caused by customer ISP's caching bad DNS information well beyond the 10 minute TTL we had set.