For example, increasing fuel efficiency of cars does decrease energy use, because fuel cost is not the limiting factor foe most car travel. Similarly, more efficient lighting, more efficient home space heating and water heating, and better weatherization of homes, all increase energy efficiency and decrease energy use.
There's only so much lighting I would ever want to use, only so much heat, only so much time I want to spend in a car. Energy efficiency is one of the most powerful tools we have to reduce pollution, because it makes all the other things easier.