[ProDigit]

If you look at the mobileread wiki page, it has been mentioned that ~DS might increase battery life.
The wiki was written for the older Kindles that didn't have a touch screen, nor screen light.
On those devices, there is a possibility that the device would last longer, not shorter, when disabling the screen saver, with the only reason that the device is consuming power, while refreshing the ads or pictures on the screen.
While having the device in ~DS mode, the cpu won't throttle up to change screen content, but remains in a permanent sleep mode.
Older devices with ~DS enabled, will show the last read page on their screen, before entering the same sleep mode as the devices that are entering into screen saver mode, with the only difference that they don't regularly refresh the screen for new content.

It also was thought that when running a device in sleep mode, the device would connect to a wireless signal (3g or wifi), on a regular basis, to download new ads (if you have an ad version).
This assessment might also not be true, but not a lot of research has been done to verify if the ad based devices download ad content while sleeping, or not.