Would be interesting to know the numbers. It's a bit like IKEA, their furniture requires less energy to produce and ship but does the resulting cheapness cause people to buy significantly more?

I don't think I buy significantly more stuff than I otherwise would just because it's convenient from Amazon, but perhaps I do.

You might still be imagining it in terms of how it is done in the US. You can have department stores on the first floor of dense housing, so people only need to walk to the store. The real estate is essentially what would be a bar or restaurant but serves more people and gives people what they need. You're right if it means turning a block that could be housing into parking and a walmart. It's better than a walmart being a 10 minute drive away from where you live, but it's only half way to how it can be (and often is elsewhere).