alt Hacker NewsThat only solves half of the cheating problem - illegal inputs from clients.
The other half is much harder to solve. For a simple example - my client knows that there is an enemy player around a corner. It knows exactly where that player is, because that player is walking, and making noise. A cheats could allow the cheater to see his opponent's player's model through the wall.
For a more blatant example, consider cheats in a first-person shooter that just snap your aim to the nearest enemy's head. This involves zero violation of the game's logic, and also makes the game completely unplayable for everyone in a lobby.
You already know where an enemy is if you hear them behind the wall, you don't need a cheat to tell you that there is noise coming from other side of the wall. The server also doesen't need to tell you they are behind it if they're sneaking. A game that allows zero home-in time sounds like a flaw in the game and something solvable on the serverside.
You can replace a playermodel with wider "sound coming from around here" if you want to make it even harder for a cheat to pinpoint a sound