My guess, and I'm sure someone more knowledgable will chime in, would be efficiencibutton a larger rocket/lift capability-
Defintely with the current 'throwaway' model, where whole rocket costs are ~95%+ cf. fuel; but I believe even with re-usable rockets (as they are aiming for) you have significant cost advantage per kg (or pound if you prefer) from a larger rocket.
So, as I see it, less cost, less launches, less messy construction (larger modules/however the beast turns out)
Maybe. Or maybe it just means a larger payload. The cost per kg could end up anywhere with new technology. At least in the beginning it might be much higher.
In the long run, you'd expect carrying heavier payloads to be cheaper per-kg (because you're lifting more payload and less rocket, relatively speaking), but carrying larger payloads to be more expensive (because you need to be using a bigger rocket). Those play against each other to some extent.
In the very short term a new technology is likely to be pricier than the existing tried, tested and refined version (especially when you include R&D costs), how long it stays that way is hard to predict.
So, as I see it, less cost, less launches, less messy construction (larger modules/however the beast turns out)