When Are Sequels And Trilogies Appropriate?

How annoying is it to wait for the third or final installment of a movie and find out that there is going to be a "part 2" you have to wait until the next year to see.  Sometimes it works and sometimes it doesn't.  Let's look at a few examples.

Recently they've done this with The Hunger Games: Mockingjay, Harry Potter and the Deathly Hallows, and Twilight Breaking Dawn.  Is it necessary for them to do this?  What is the motivation for setting up a scenario wherein there is a part two to a sequel or trilogy?

Money and greed seem to be the first two answers coming to mind, especially with The Hunger Games franchise.  Not knowing anything about the story at the time, I was intrigued to read the books after watching the first movie. The final book was about the same length of the other books but not as good.  As a matter of fact, I felt like the author was rushed to finish the book. For how bad the book was, I couldn't believe that they would make the film adaptation a two-parter.  Part one was especially drawn out; one movie would have been better in this case in stead of two.

With a film series like Harry Potter, I'll have to go with the old saying that the books are better than the movie. That being said, there's so much detail in the books that they don't have time for in the movie unless the movie is over three or four hours long.  I think that the Deathly Hallows having two parts was acceptable because it had a good pace, they were hitting on critical points, and they didn't stray from the story.  The films didn't have everything from the book but it was enough to keep the viewer satisfied.

The new Hobbit movies royally pissed me off.  After reading the book as a kid and watching the cartoon movie adaptation, for them to make three movies out of this book is just ridiculous and greedy.  It was good going back to Middle-Earth and reliving the memories of our favorite characters from Lord Of The Rings, but there were so many parts in these movies that were long, drawn out, and boring. Boring to the point where I fell asleep multiple times during the second and third films. I could understand having two movies, but definitely not three.

Are there anymore movies out there that hve multiple sequels that are not necessary?

Do you think this trend will grow and be part of movies from now on?

Let us know what you think.