Developers of technology pursue efficiency relentlessly. This is done for a variety of reasons: Efficiency is readily quantified and lends itself to comparison between designs; a preference for efficiency seems simply rational (who wouldn't prefer a more efficient car over a less efficient one?); increases in efficiency increase sustainability.
The last point seems quite plausible. If you substitute a more efficient car for a less efficient one, then the new car will deliver its service while using less fuel. The driver saves money and the supply of gasoline is extended further into the future. A win-win!
A problem with this logic was pointed out by British economist William Stanley Jevons. He argued the increasing efficiency actually increases consumption. In a nutshell, getting more work from a resource effectively decreases its unit price, which stimulates consumption. More efficient cars mean longer trips, more trips, and more people who can afford to drive.
However, the devil is in the details and the reality of the so-called Jevons' Paradox has been disputed. So, it is interesting to read a recent article by Magee & Devezas (nicely summarized by Michael Irving at New Atlas) suggesting that the Paradox seems to be ubiquitous.
Employing a general economic model, the article examines the consumption of 57 material resources as diverse as aluminum, silicon, and wool. In brief, it concludes that increases in consumption have outpaced gains from efficiency in every case.
Consider the case of hard disk drives (HDDs). Recent years have seen phenomenal increases in efficiency, that is, the ability to store information with a given amount of HDD material. Surely, this increase in efficiency would imply a decrease in the amount of HDD material used. Yet, the consumption of HDD material has increased:
...over time—despite rapid improvement—the technology results in more materials use—not less.
As the cost of HDD goes down, people store more data, of more types, and more people get in on the act, resulting in an overall increase.
This result does not mean that efficiency increases are evil. Instead, it means that they will not deliver reductions in consumption that may be required for various sustainability goals. That may mean changes in lifestyle, something that is harder to measure and perhaps also harder to achieve.