Moving along the Plot

Plot xp means you reward the players for moving the plot.
This got me thinking about “units” of plot, in order to dole out xp for those units.
In a general sense an RPG adventure is like a movie. A movie can be broken up into sequences and further into scenes.
Using the RPG – Movie analogy:
A movie is an adventure or series of adventures; we need to rescue the princess from the evil Prince Humperdink.
An act or Sequence is a smaller part of that plot; we need to resurrect the Dread Pirate Roberts.
A scene is the smallest unit and comprises of a single combat, a few skill checks, etc; we need to use our diplomacy to convince Miracle Max to resurrect the Dread Pirate.

So what gets the reward, a scene? a sequence? an adventure? A combination of the three?
What if the players chase a wild goose, creating unnecessary scenes?