The converse of this would seem to be: "If you need the word to preserve rhyme and meter in a song, poem or ballad, go for it."

Alternatively, it seems to me that having a character say it would at least lay the blame for the extra word at the character's door. After all, we know that how we speak is (generally) not how we write. e.g.:

"I shall pursue you to the ends of the earth!" Draco said to Harry as wizards in white coats dragged him through the Great Hall and away to St Mungo's. "I shall scream out your name and my lusts for you on every street corner from here to Durmstrang!"