I guess it is the case where the info begs to the player, the player reaction time is in tens or hundreds of milliseconds (time to render the image, display it on the screen, player to see, move the mouse to aim and shoot) versus an aimbot that does not need to wait and can react in a few milliseconds. This is cheating if the cheater's aimbot is using an advantage normal players don't have (unless everyone is using aimbots and this is no longer a human-played game but a bot game).