The current incarnation of this system only uses four robots, but it's been designed with scalability in mind, and it'll work for all different kinds of hardware. All of the benefits of swarm robotics apply here: you can deploy lots and lots of small, cheap robots that can work together to efficiently perform much of the work that would take one big, expensive robot a very long time to execute. And if you lose one or two individuals out of your swarm to mechanical issues, moonquakes, Marsnadoes, asteroid impacts, meteor impacts, meteoroid impacts, meteorite impacts, rogue AI takeovers, alien abductions, climate change, budget cuts, untrustworthy Nigerian princes, or an attack on the Deep Space Network by crazed wombats, the mission will still likely succeed. Hooray!
Next, NASA will add some robots to the mix that actually do know how to get some work done. The plan is to incorporate RASSOR, "a concept robotic vehicle evaluating designs for a future craft that could work on another world."