I used to root my android phone to limit battery charge + adaway. But recently I finally gave up with rooting due to all the restrictions that comes along with it.
I thought it wasn't possible except by rooting or external control. I've just been doing it manually but figure on adding an automatic controller sometime.
Afaik yes, kinda. 100% likely doesn't mean that the battery is 100% full it might mean 99% or something. I have no idea how much they reduce it but the point of this is to be able to reduce it even more. Which would be better for your battery.