Examining Franchise Movies and Sequels

Do you remember that time in "Back to the Future II" when Marty McFly travels to 2015 and finds that there are still future incarnations of "Jaws" movies playing in the theater? It was a good joke - and a funny one, mainly because it's true.

Many franchises extend for multiple sequels. Examples include "Indiana Jones" (and its sad attempt at a comeback years later), "Police Academy" (there are seven), and "Pink Panther" (with ten). There seems to be a difference between movies like this and the epic, universe-encompassing franchises such as "Star Wars," "Star Trek," and "Lord of the Rings." However, some movies have made me think about the legitimacy of sequels. Do they exist to tell a story - or just to get more money out of the audience?