[Psitticine]

It means you want to take a Cold 3 setting on your scales when you design your Pretender. If you don't, and instead stick with the default Cold/Heat 0, you'll be three steps away from your nation's preferred temperature and suffer a 15% income loss and a very painful 30% supply loss. Your opponents will also be happier, since it would normally be they who took those penalties when trying to take one of your provinces. Since moving away in either direction from Heat/Cold 0 gives you points instead of taking them, you would also be shortchanging yourself design points that could be spent elsewhere.

On a side-note Caelum versus Abyssia can be an interesting Dominion-shoving match because of the temperature effects. Abyssia likes heat, so they have even more of a penalty fighting in Caelum's cold, but Caelum has similar penalties fighting in Abyissa's heat, so the temperature (as altered by the Pretenders of the two nations) becomes a vital thing.