Controlling backlight might be necessary for some contexts. For example, if you want to show a static picture, it doesn't really make sense to refresh the display all the time - and that's what you'd need to do currently, given that, in case the backlight is turned on and a timeout is set, it's global and affects all apps. So, there's no way for an app to signal that turning the backlight (in case of OLEDs, the display) off is unwanted. Of course, any changes only need to apply to that specific app that requested the change, as in, only while that app is running - not any other apps. The output proxy system (as designed for #8) will probably make implementing this easy.
Controlling backlight might be necessary for some contexts. For example, if you want to show a static picture, it doesn't really make sense to refresh the display all the time - and that's what you'd need to do currently, given that, in case the backlight is turned on and a timeout is set, it's global and affects all apps. So, there's no way for an app to signal that turning the backlight (in case of OLEDs, the display) off is unwanted. Of course, any changes only need to apply to that specific app that requested the change, as in, only while that app is running - not any other apps. The output proxy system (as designed for #8) will probably make implementing this easy.