I agree that in some cases it can add something, when things are not supposed to be sung, but more spoken/cried. Mostly scenes where someone is dying benefit from it, with all the breaths etc.
In fact, madonna's final scene was recorded live:
http://www.youtube.com/watch?v=5R0P1Bwzhug It basically sounds the same as all the songs in the Les Miserables film and that is too much if you ask me. Imagine Madonna would sing the whole film like that. The problem is that that particular music (Les Mis, Miss Saigon) demands great singing voices and the uplifting notes and the placement of the sung notes create the emotion and storytelling too, that is what musical is. Especially combined with great editing instead of using just 1 close up for each song. Singing the first word of a sentence and then speak or sigh the last word of each sentence is not the solution of singing in a musical film (Although Hugh Jackman thinks so).
I believe that the scenes I posted above would have never been so great if recorded live. And vice versa, I think a lot of scenes in Les Mis could have been much better.
I see moviemaking as more than just putting a camera in someone's face and let him/her sing the song a couple of times. I can imagine that for example "The movie in my mind" from Miss Saigon can turn out very average if done that way, while with the right editing, cinematography and studio recording with the soaring notes, including singing along live for the acting can make this scene exceptional. Raw emotion for the viewer comes from other things too.
Updated On: 1/9/14 at 08:24 PM