I've mentioned earlier that by the '70s, the Broadway musical was basically a director's medium: from that point on, musicals would be largely about the way they were staged and the conceptual gimmicks that the director came up with. Another part of this was that songs were increasingly written around the staging, whereas in the past, the director would build the staging around the song that was written for a particular spot.
So in a Rodgers and Hammerstein musical, R&H (the producers as well as the writers) would come up with a song, and leave it to the director to figure out how to execute it. Joshua Logan, the director and co-writer of South Pacific, had to come up with physical gimmicks to maintain interest during a song -- like having Liat act out the lyrics of "Happy Talk" while her mother sings the song -- but what he didn't do was come up with a stage picture and ask the songwriters for something to fill it.
By the late '60s and '70s, you have more and more songs whose music and lyrics are shaped by the staging, rather than vice-versa. A lot of the songs in Bob Fosse musicals are like that, with the melody shaped to fit the typical Fosse moves instead of Fosse coming up with dance moves based on the music. And Stephen Sondheim became Hal Prince's favorite songwriter, in part, because he was willing to write long numbers around Prince's stage pictures. (It's said that Sondheim didn't come up with the Act 1 finale of A Little Night Music, "A Weekend In the Country," until Prince had already blocked the whole scene.)
Here's a good example of what I mean, Sondheim's personal favorite of his songs, "Someone In a Tree" from Pacific Overtures. This is a song entirely based on a stage picture: instead of seeing the signing of the treaty of Kanagawa, we get it from the perspective of onlookers: someone who saw the whole thing from a distance when he was a ten year-old boy (but couldn't hear what they were saying), and a samurai hiding below the treaty house (who is listening in case he's summoned for backup, but can't see what's going on). We have the narrator (Mako) and the old man in the present, and the young boy and the samurai in the past, and the lighting picks out little fragments instead of showing a big scenic picture all at once. That's all built into the song, and so although the song does work on a recording, it really isn't designed to work separately from the staging. And instead of the director coming up with stage business to sell the song, the song incorporates stage business that is necessary for the scene, like the tree climbing. It is, in part, a song that expresses the director's vision.
Here's the original Broadway cast:
Speaking of Pacific Overtures, the same uploader also has the original cast doing the first number from the second act, "Please Hello" (where various Western countries come in and force Japan to trade with them). It's one of the weaker numbers because the music consists of lame parodies of Sousa, Gilbert and Sullivan, etc., but the lyrics may be the most intricately-rhymed of all time.