The "rebound effect" postulates that, as energy efficiency goes up, the cost of using energy consuming products becomes less, which in turn leads us to consume more energy. So, for example, if your car gets better gas mileage, you will just drive it more.
But this argument is flawed in several respects. For example, in T.O (where I live) driving more means being stuck on the 404/401 longer, which tends to decrease the amount of pleasure associated with the whole experience.
In other words, driving is not like sex: you wouldn’t necessarily do more of it if you just had more energy.
Click through link above for scholarly discussion.