There's some discussion of this in Starbucked, i.e. why Starbucks stores open across the road from each other. Part of it is if people are already going to that location for coffee, having an extra Starbucks and shorter lines will incite them to go more often; the illusion of choice. I don't really recall the rest of the reasoning as it seemed somewhat spurious, but the fact quoted in the book, that when a Starbucks opens across from another they both do better business than the solo shop, is quite remarkable.