In fact the power consumption of the Haswell desktop parts is actually *higher* than that of Ivybridge (bizarrely). So even any thought of power saving / green issues / electricity cost etc goes out of the window.
The only benefit is a 2.9% CPU speed improvement. Of course most operations are not only CPU bottlenecked, so +2.9% would be the best you'd see and usually less than that. i.e. undetectable unless you are trying to specifcially measure it.
These two posts tell the story. Get it. At least you've built up some anxiety, so when you get it, you will be further amazed. Hunger is the best sauce