I agree with Stephen, want is the point of using a composer if you don't let them see the footage before composing, you may as well use library music.
The only time that having the music before the edit works well, is when you're using existing, recorded songs and the song is part of the narrative. That way you know before shooting, that you want to cut to that song.
I think because a lot of filmmakers have an almost music video approach to production, it seems natural to them to cut to the music, but if I remember rightly, that practice doesn't go back much further than Easy Rider.
The only time that having the music before the edit works well, is when you're using existing, recorded songs and the song is part of the narrative. That way you know before shooting, that you want to cut to that song.
I think because a lot of filmmakers have an almost music video approach to production, it seems natural to them to cut to the music, but if I remember rightly, that practice doesn't go back much further than Easy Rider.