How does The Princess Bride use its framing story to influence the tone of its embedded story?

The Princess Bride's goal above all is to keep its audience from taking it too seriously. This is a difficult task given the sometimes depressing or scary moments present in such an epic tale. To counter any over-investment on the viewer's part, the film frequently takes us out of the moment through an interruption by the grandson of the grandfather in the framing story as a way of paralleling their experience with our own. When Buttercup is about to be eaten by a giant eel, when she dreams that she actually did marry Prince Humperdinck, or when we're about to get the sweet, satisfying final kiss from her and Westley, we are suddenly torn back into 1987, a reminder that this is a story and nothing more, and that treating it as importantly as real life is fool-hardy and missing the point of an entertaining fictional tale.