You got the use case right, but I think you're still thinking about it wrong. In-use public DNS changes aren't something that just crop up and need to be done immediately.

Eg. Five days from now, I'm going to make an infrastructure change that will affect public DNS. Today, I lower my TTL on affected records. Five days later I make the public changes, still using the lower TTL. Once I am satisfied my change will stay in production, I modify TTLs to be more sane.