He means exceptions are not for common control flow that shows up everywhere, like a return value. You want an exceptional control flow change when your hard drive runs out of storage, but you don't want exceptional control flow change when your hashtable doesn't have the key you're looking for.

The categories and frequency of these conditions are very different.

An exception would be if someone tried to get the parking status for "Blarghsday" from the function or some other impossible state (We all know time is weird[0])

If the expected operation is to return parking allowed status for a specified date or a weekday, I'd expect the function to return true or false unless the input is malformed (Actually I'd prefer it to return some kind of object that can give more context to the true/false, but I digress).

During normal operation it should never throw an exception. Because if I get an exception, I'll most likely either throw it up the stack or log an error, which will ping someone in PagerDuty if it happens too often.

[0] https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b...