Hopefully Jim will clarify too, but I'm pretty sure he meant that the Driver Action or Decision scene/sequence will usually (always?) coincide with one of the signpost/PSR beats.
Here are some examples:
Example 1, Star Wars (1977): An Imperial Star Destroyer attacks a diplomatic vessel -- as a validation of their ultimate power, the Empire does something that it is not permitted, making it understood they can get away with whatever they want now. (Action, Permission while Understanding, OS Problem Test)
Example 2, The Princess Bride: Buttercup and Westley suffer a twist of fate when his ship is attacked by the Dread Pirate Roberts, who never takes prisoners, so Buttercup gets the idea that her true love is dead. (Action, Fate while Conceiving, OS Problem Evaluation (i.e. making a poor evaluation of Westley's fate))
Example 3, The Matrix: Through an investigation of Neo and his hacking activities, Morpheus decides that Neo is The One, though some of his team are skeptical*. (Decision, Investigation while Doing, OS Problem Disbelief)
* all this is implied in the first minute, in a brief conversation between Cypher and Trinity
I don't know that this is required for a complete story, but it sure has a great feel to it. It also worked really well for something in my own story that Jim helped me with recently (see my last post above).