Sometimes that error was being smuggled in another broader error to begin with, so if the caller is having to go spelunking into the .description (or .message)

Sometimes that error was being smuggled in another broader error to begin with, so if the caller is having to go spelunking into the .description (or .message) to know, that's a very serious problem. The distinction I make is: if the caller knew about this new type of error, what would they do differently?