The car always has to be capable of driving safely and avoiding collisions locally. The human operators are being asked occasionally to help with some higher level, longer term decisions. As a random example, if there's foreign objects blocking the road, the car has to be able to stop itself before hitting them, but it might phone-home to a human to decide if a u-turn is appropriate.

My understanding is that Waymo's remote driving is not direct control of the car, for exactly these reasons among others. So human operators don't have steering wheels or joysticks. Instead the humans can give something closer to advice (e.g., "pull to the right and stop") that the car can accept, modify, or reject.