Question for the experts: what are the tests and analysis that we cannot do via a rover-based lab and hence need to send the samples to Earth? Asking out of curiosity (pun not intended!).
Simple answer from a space nerd: Rovers are small, light, and have very little energy. So what we can't do is anything that requires a large or heavy device or anything that requires significant energy. They break/fail. They take forever to make happen. Want to burn 20kg of soil to see if there's any trace of specific elements? You'll need a furnace. Those are both heavy and high-energy. You could do a smaller scale…
If Starship meets its performance targets, it’s first missions will bring hundreds of scientists to a Mars, with thousands of tons of equipment and supplies. In-orbit and in-situ refueling are game changing technologies that will literally reduce the cost of deep space manned missions by a thousandfold.