Beyond picking up rocks, the human can traverse the terrain more easily and s/he can climb up and down really steep slopes - even ones at a nearly 90˚ angle. Whether you'd want the human to do that due to safety concerns on an alien world is another matter, but the amount of terrain accessible to this being is far larger than most billion dollar robots.
Oh and the human being does all of this while being powered on tuna sandwiches. They might be expensive to send to Mars, but once they're there humans can explore a larger area than all rover missions combined in a single mission.