The basic problem with intelligence intercepts is how to use them without alerting the targets how you know. Fortunately for the spooks there is usually enough noise in the system for them to hide behind.
Another problem, often overlooked, is intelligence intercepts are often incomplete in some critical manner. In the movie "Tora, Tora, Tora", US cryptographers had deduced accurately the Japanese were going to attack the US. But the decrypts of foreign ministry communications did not include military details about timing and location of the attacks. The problem the interpreters had was who were the initial targets and when were they going to be hit. This was actual historical problem, the US know something big was going down but did not know when and where.
In WWII, the Admiralty Submarine Tracking Room used Enigma decrypts, traffic analysis, and shrewd guessing to anticipate the German moves in the Atlantic. The primary interpreter called his analysis "working fiction" because of the varying degree of guessing involved. Often it was shred guessing that was important. Enigma decrypts were erratic through WWII, with the Germans regularly changing the settings, number rotors, etc.