'Course they'll move faster. Just like if you're waiting for a lift, pushing the button repeatedly will make it arrive faster. :)

But seriously, they're just being careful to observe the strict New York City Vehicle Horn Code, under which it is illegal to honk your horn except to communicate one of the following emergency messages:

1) The light is green.
2) The light is red.
3) I hate you.
4) This vehicle is equipped with a horn.