I always see rhyme as a mental pause for breath - not for the singer but for the audience. They anticipate the word and have more mindspace to take-in the meaning between the rhyme. Without that punctuation how is the song going to allow the listener to perform this trick? There are tricks, and music plays a big part but the song has to be crafted well, both lyrically and melodically to work the trick. Witness shanties. Unless the meaning of the words is largely unimportant and the voice is to be treated as another instrument, then who cares? I assume French poetry uses rhyme. English has about twice the lexicon of other languages (certainly French) which makes the choices more adaptable to rhyme.