One of the benefits of import substitution is that a country produces and consumes its own goods.
Even on a regional level within a country, import substitution leads to increase localization and sustainability as local consumers buy increasingly local products.
As large international players are removed from a market, and thus competition, local companies can take over. For example, instead of buying a foreign brand of beer, a consumer can buy beer from a local brewer.
The local product, especially if it relies on local ingredient or historic local know-how, can be competitive in price as the transport costs are much lower,the product "fresher", more tailored to local tastes, than something sourced from far away or from abroad. This also makes the product and the business model more sustainable.
This leads to money flows remaining within a region and helps to the region's development. Therefore the regional authorities and businesses should push for "parochialism economics" to make consumers aware of local goods, and to send the message that by spending on locally produced goods, money will remain locally and their local communities will improve economically.
Within a country, healthy competition between neighbouring regions stimulate the overall efficiency of the economy. One example would be Irish vs Scottish whisky, which are neighbours, if they are not strictly regions within the same state.