Mostly for when your card has more power then you are using or your screen can handle. If you all ready can't turn stuff up to max in your games it probably won't work for you very well. Pixel density of your screen will also affect how well this works for you.
Saw this quite a while ago. Isnt this the same thing as 2x super-sample anti aliasing though? Also be sure to set the monitor scaling to your GPU. If the monitor handles resolution scaling then it will create more input lag.
