But those are no valid use cases which was my question. So there are no valid use cases at all?
Why is this not valid?
If your DNS hosting provider charged you per query (some do, especially when adding features like health checks & load balancing), then it might make a big difference.
If a load balancer or DC fails we need to ensure traffic moves away fast. Similarly if you want to take a system out for maintenance or perform migrations.
Well, if that's the case, you better have your redundant systems on your normal DNS entries, because there is no chance you will distribute new entries over the internet in 5 minutes, whatever value you specify at the TTL.
Easily 90% of new connections will move following the TTL. Of course, some traffic got a DNS result once in 2003 and is going to use that forever. If it's important traffic, you can trace it and follow up with them. If not, you do the best you can and let the rest go.
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Please tell me you're not testing in production.