Depends how you define "making an area poorer" If you take everything (social/economic) into account then there is no doubt that are a bad thing. Who really wants to have to make their way to an big ugly retail park in the middle of nowhere? If you have not got a car then you either need to use public transport/taxi or walk which basically kills any savings you might make. In the city I live now in Scandinavia I'm never more than 5/10 minutes walk from a major chain store as they are not allowed to be over a certain size and therefore you will usually find a well stocked store in every neighborhood.