What's the rationale? It should be described in the README.md IMO

That's good feedback. I just added it to the readme:

> "PanicLock fills a gap macOS leaves open: there is no built-in way to instantly disable Touch ID when it matters. Biometrics are convenient day-to-day, and sometimes preferable when you need speed or want to avoid your password being observed. But in sensitive situations, law enforcement and border agents in many countries can compel a biometric unlock in ways they cannot with a password. PanicLock gives you a one-click menu bar button, a customizable hotkey, or an automatic lock-on-lid-close option that immediately disables Touch ID and locks your screen, restoring password-only protection without killing your session or shutting down."

I've more details on the apps landing page - paniclock.github.io

A person might use it to stop someone getting into your computer through certain types of physical coercion, forcing your finger to the reader, or (much less likely but I’m sure security services know how) a copy of your fingerprint.

But it isn’t a why, it is a what. That what is a tool that lets you quickly disable Touch ID for whatever reason you want to.