I really like some the changes the films made to Pippin's story. Successfully tricking Treebeard into seeing the true scale of what Saruman had done is in keeping with his character from earlier in the story, but still a big step for him to take in terms of thinking things through and also a huge contribution to the overall battle. Sneaking up to light the beacons of Gondor is cool too, and reflects Bilbo in the Hobbit to a degree