Another thing I don't like so much: an article about a single poem or song, or a book on a poet that only deals with a small part of their work. I'm sure I've done it myself, and it may be justified with super-canonical folks like Lorca.
My thinking is that this is a lot of weight to exert on a single object: I prefer to learn about many poems and songs, or whatever object of study it is, at the same time, with some comparative ideas thrown in the mix. I think I associate this with the laser focused narrowness of some very young scholars. Or the laser focused narrowness of specialists on canonical authors. It isn't horrible, just not my preference.
Novels and films, yes, you often will want to write an article or chapter on single novel. Not so much a short story. It's about a certain sense of proportionality. I remember a dissertation where each chapter dealt with a short story.
Remember the iceberg approach (Hemingway). You don't have to say everything you know (and you couldn't anyway). You don't want to give the impression that your knowledge is so thin that you are unaware of the larger picture.