Historically, there are so many incentives to buy locally that no one had to make any kind of point to do so: the energy subsidy was not available to make packaging, transport, inspection, retail facilities, etc., so cheap that local goods could be outcompeted by those shipped in from across the planet. The drive to deliberate globalization, however, has according to Amory Lovins flipped energy economics on its head: it is now clearly more profitable to waste energy than save it, a quirk of the primitive energy-and-diversity-ignoring neoclassical economics.
Given this situation, local purchasing may amount to moral purchasing - at least insofar as one is refusing to exploit the most obvious subsidies to waste energy and resources. However, if local agriculture or manufacturing is itself reliant on heavy energy subsidy, this may be counter-productive, and penalize the more efficient, employment-intensive, methods of responsible global growers. Thus it is not wise to consider local purchasing as necessarily morally superior, except insofar as one knows the products to be produced using methods that don't rely on some oppressively produced inputs, or those which create pollution.
Import substitution is a deliberate industrial policy or agricultural policy of replacing goods or services produced on the far side of a national border with those produced on the near side, i.e. in the same country or trade bloc. It has been a feature of policy in many countries, and is a first step towards local purchasing as such. In small countries, it amounts to the same thing.