Maybe it was a fix for supply problems, but unless the IC province sits directly on a supply line, the supplies often appear to move back home. Possibly minus supply tax, just to make it more "fun".
Curious. So the idea being that it opens a supply network in a country to keep active supply lines going to different parts of the country? That makes sense -- instead of having to wait for supply lines to establish themselves across the country, some predefined lines are already in place.