They have a lower unit cost per item to the individual. Sometimes. But typically only if you ignore transportation and storage costs. And often infrastructure costs are effectively billed to society.

Consider, I can literally walk to the grocery to buy beer. I suppose I have to replace my shoes from wear, but no upkeep or gas on my car. No miles of road that need maintenance to subsidize my trip to the store.

Now, yes, there are miles of road to subsidize getting the store supplied. But that is shared for all people supplied by the store. Same is true, of course, for the trips to the store, but again, my side of that equation is zero. Which is all part of what makes me argue it is more efficient.

And again, complicated with general scale making most observations necessarily simplistic.