What are the pros/cons of the short story/short poem in communicating ideas?
It is short, and sticks in the mind. Crossing the Bar comes to my mind, I first heard it in Junior High School over fifty years ago. Poe's The Raven is another. O'Henry's story The Gift of the Magi is another. We remember these because they are short, to the point, and are powerful works of thought. Finally, The Gettysburg Address is another which is remembered because it is short, and powerful.
The con, I suppose is that complicated intricacies cannot be developed.
Short stories and poems are great because the point is quickly made and stays with one..... however longer stories have more time to develop characters and motivation. We learn who they are, why they behave as they do and are able to identify with them.
Novels like Tom Sawyer, Catcher in the Rye, The Crucible, Don Quixote Give us an understanding that others share our problems and that we have common goals.