Some more recent benefits that spring to mind are
One problem is how to balance words and images - if the images are dazzling who's going to bother with the words? On the other hand, one doesn't want the images to slavishly follow the words, showing a picture of a tree whenever the word "tree" appears. I suspect a successful movie poem needs to be watched a few times, so the WWW or CD/DVDs are perhaps their most appropriate media.
For examples, go to
Alternatively one can use pre-existing movie clips. The original soundtrack can be muted during the voice-over, speeded up or replaced by music.