In an interview with Gamereactor, Hitman: Absolution's gameplay director, Christian Elverdam, has explained the addition of the controversial ability to see through walls.
The new ability, called instinct, augments several abilities in the game. For example when wearing a disguise, it can allow you to bluff your way through situations, where in the past, you would alert guards and therefore ruin your mission. Instinct also allows you to see the paths and positions of enemies through walls when activated. The reasoning behind this, according to the gameplay director, is to allow users to know the consequences of their choices.
For example, if you've killed someone clumsily, rather than relying on trial and error, and getting caught and having to restart from the last checkpoint, instinct allows you to see the path of the enemies that are after you will take, and make an informed decision. So instinct allows you to see the consequences of your actions before you make a decision.
The effectiveness of this power is dependent on your difficulty setting, so if you're a purist, play on hard mode.