[tinkthank]

Originally posted by Graeme Dice:
Both allow for your heat scale to spread outside of the regions where your dominion exists. Without them, you will only shift the heat scale in a province that has a high level of your dominion.

This is how its description reads. It seems almost like a type of "restless worshippers" for heat/cold only.
However, despite the description, it seems as if the effects are negligable, although I suppose this would be hard to demonstrate.