MLA Signal Phrases

In writing class, I was recently assigned a research/classification essay in MLA format. I was already very experienced with MLA's style and citation format from English 101 at Black Hawk. However, this essay required that I use signal phrases before the parenthetical citations. I'm fairly certain that MLA doesn't require it, but the professor was very adamant that we use them. They're very nice in that that remove the requirement to put the author's name and book title in the parentheses, making them lengthy. However, they have the downside of placing bibliographical information right alongside content, which I personally find to be unattractive. I think it's better for text to be laid out in such a way that a machine could separate bibliographical data from real text.