My earlier reply got cut off when I went back in to fix a typo, but I'd love to mention Sondheim intentionally subverts the expectations of the classic "I Want" song to weave the protagonists' desires more deeply into a musical scene.
In the case of SUNDAY IN THE PARK WITH GEORGE, we learn what the protagonist wants by having someone else sing about it. Through Dot's opening song, we learn that George wants to do something new, wants to objectify his girlfriend, and is obsessed with his craft.
And in COMPANY, we brilliantly figure out what Bobby wants by seeing what a fish out of water he is. One of these things is not like the other; his friends are all in relationships. And they're all happy... or so they seem. It's certainly not a classic "I Want" song. But by the end of that number, we know what Bobby doesn't want.