[iMore Question]

May I ask what is the USB-C used for and how does it work?

[phreddyl]

It's the new standard in usb plugs. It's reversible so you can put it in either way. Many newer products like the new MacBook use this.
Here is Wikipedia definition https://en.m.wikipedia.org/wiki/USB_Type-C

[anon(9602380)]

On the new Apple TV it’s used for diagnostic purposes. Most users are unlikely to ever use it and Apple has deemed it unnecessary to include a USB-C cable with every purchase of the new Apple TV. In addition to the Apple TV unit itself, the Siri remote, and some documentation, a fourth-generation Apple TV comes with no USB-C cable. (A USB-C cable was in fact shipped by Apple with the original Apple TV developer kit, but it was no longer included in the succeeding round of shipments of Apple TV developer kits.)

The USB-C cable offers the only way for the new Apple TV to interface with a computer for things like taking screenshots of screen recordings from the device and, more important, restoring the device to factory settings via iTunes (in the event that over-the-air restore doesn’t work). Most users will never need, or even want, to plug their Apple TV to their computers.