depending on the caliber, the ACI on long distance shots on uneven ground becomes crucial whether shooting targets or at game.
the "poke and hope" method of holding under or over game isn't very ethical when shooting from / at elevated positions, and depending on the distance and slope can result in several inches to a foot of difference compared to flat ground.
of course just having the tool on the rifle doesn't mean much if you don't know how to use it. one should practice from elevated positions or at elevated targets at distance, and a proper data book with proper dope and a calculator to make an educated adjustment is just as crucial, and goes hand in hand with the ACI.