Being able to do something like this is important because being able to refill on-site means you don't need to bring enough oxygen with you for a return trip, b

Being able to do something like this is important because being able to refill on-site means you don't need to bring enough oxygen with you for a return trip, but we should remember this is nowhere near sufficient to start terraforming the Martian atmosphere. The biggest issue is still the density. It is well, well below the limit at which human bodily fluids boil at normal body temperature. Getting the molecular mix right might eventually be a concern many, many centuries from now, but first we just need more gas at all. It doesn't help that Mars continually loses more atmosphere due to solar wind because it doesn't have a magnetic field, too. I have no idea what we could realistically ever do about that, but solving that is a prerequisite to ever having permanent colonies that don't need to live underground forever.