What are the benefits over the traditional safety driver on standby whithin the otherwise self-driving car?

I can see that this is more future-compatible, the "drone" is smaller than a car, so, when you can lose the driver you will be able to shake off the whole shadow vehicle and have less mass overhead.

Edit: also, PR. The pretty pictures of the obviously driverless vehicle are almost inherently misleading.

Anyone can see anything else?