The amount of fuel limits how far you can go in terms of delta-v and mass. So, if you have to have all the fuel on board when you launch from the ground, there'

The amount of fuel limits how far you can go in terms of delta-v and mass. So, if you have to have all the fuel on board when you launch from the ground, there's only so far you will go and so much you can take with you. The point of going back to the moon is not only just planting a few more flags but actually taking some meaningful amount of resources there to ultimately be able to build a moon base. Same with Mars. And we might want to take some more stuff back (rocks, minerals, whatever). So, that requires fuel as well. The point of refueling is getting to orbit and then topping up all the fuel you lost getting there (i.e. most of the fuel because getting out of the atmosphere takes a lot of energy). Starship when it starts flying will be by far the largest amount of mass we can get to orbit. Like upto 150 tonnes or whatever the maximum payload is going to be. So, that amount of fuel would enable large amounts of mass to be accelerated to a path to the Moon, Mars, or wherever way beyond what would otherwise be feasible. And with a reusable launch vehicle, it actually gets doable from a price point of view as well.