Songs are amazing things. They're like little aside monologues/sililoquoys that allow the audience to hear and feel what the character is feeling.
Take for example Les Miserables. Few musicals can deliver the emotional power that this one does, and it mostly lies in the solo numbers. Like Javert singing just before his suicide. Were we to simply watch a film on Les Mis, and not hear such powerful words, even if they are just paraphrased and spoken instead of sung, we wouldn't know why he's killing himself because he let Valjean go. And Marius' song, one of my all-time favorite pieces in history, how else would we be able to feel his pain at losing his friends, and the guilt of being the "only survivor?"
"Oh, my friends, my friends, don't ask me what your sacrifice was for!"
Those words are haunting enough without the music, but the mourning bassline makes you feel the pain even moreso, not to mention the actual tone of the singer helps too, a great deal.
When choosing the perfect Phantom for Phantom of the Opera coming out in September, someone on IMDB put it perfectly:
Just ask the actor to sing this:
"You alone can make my song take flight, it's over now, the music of the night."
Whoever has the best emotion singing that is your man for the Phantom.
