About 50% less LEDs needed and the LCD panel itself uses less energy in general.
This has several advantages:
- 50% less LED lights (probably the most inefficient component in a tablet/phone), device can become thinner
- Slightly more energy efficient as a LCD panel
- As a result a smaller battery is needed (and the device becomes lighter)
- As a result of this the entire device can be thinner (and thus even lighter, because less aluminium is needed (in case of an aluminium back)).
It's like a domino-effect: take out the highly inefficient display and replace it with a more efficient display, thus less LEDs are needed, thus the energy usage comes down, thus a smaller (and a less weighing) battery is needed, thus the device can be slimmed down and thus you get a thinner, lighter device that offers you just as much as before.
And since less components are needed (50% less LED lights, lower-capacity batteries) they might even save some money. IGZO displays are only slightly more expensive than the regular displays.
Edit: Oh, and IGZO panels don't improve image qualilty or something like that. They just allow Apple (and others) to build smaller, thinner and lighter devices.
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No one wants to go down on battery life, though.
