By revealing what is known in diplomatic circles, the depth of surveillance can be surmised. In some cases, this could lead to physical harm to those who provided the data. In all cases it allows the enemy to profile our security capabilities.
Note that this is true even for information which does not surprise us. For instance, in the case of North Korea supplying some number of rockets to Iran none of us is surprised in the least. However, if the number is precise and thought by the Iranians to be a "secret", then they will start looking for how we could have known. Furthermore, it may key them in to other information which they had previously presumed to be a secret which now they will presume to be compromised.
In almost any game, you are at a disadvantage if your cards are shown. It is hard enough playing "defense" against these bozos without someone exposing our playing hand.
Then I’d say it’s the Chinese at hand.