Robots are hard to build, but they can go places like Mars where it would be more expensive and more risky to send humans. Computers need power, but this is easier to generate in electrical form than by creating a supply of human-digestible foods that contain a variety of nutrients. Machines are easier to shield from radiation, don’t need exercise to prevent muscle atrophy, and can generally be made more hardy than biological astronauts.
But in the long run, it won’t be just in space where machines will have the advantage. Biological neurons transmit signals at 1 to 120 meters per second, whereas electronic signals travel at 300 million meters per second (the speed of light). Neurons can fire at most 200 times per second, compared with about 2 billion times per second for modern microprocessors. While human brains currently have more total processing power than even the fastest supercomputers, machines are predicted to catch up in processing power within a few decades.