Tracking the location of the truck delivering your package sounds pretty useful. And UPS/Amazon already do this. But publishing the individual personal location of each of the 500,000 USPS employees in real-time while they're working... is a bit different.

If you track them while working you’ll focus on hourly productivity rather than annual productivity and customer satisfaction. My postman has literal love letters by children written on houses on the block, makes sure you never loose any important documents, and so generally amazing, and I’m sure if you looked at his « number of houses per hour » metric it’d look bad.

If we're talking about public tracking: package theft