In this scenario, what you need is a label to distinguish the book you read from all the others.
But a title can have several functions. It can be direct so you know exactly what to expect or it can give you a hint of the contents, alerting you but not explaining completely. A title can also contribute to the meaning, add a layer. You might call your painting, story, poem, collage, "The White Squares," for example, and it could be about the origin of confetti, places in predominantly Caucasian cities, a look at chess, a visit to the Untitled Library, or a kind of pastry. A title can evoke an image, idea, concept. It can be a pun, a play on words, a metaphor or simile. A title can add depth and/or clarify the context. For artwork, particularly, a title can situate the viewer, give the viewer a starting point, or add a new thought. A long title and/or a seeming non-sequitar might reveal the maker's attitude or sense of humor.
In the book Women Artists and the Surrealist Movement (a very clear title) by Whitney Chadwick, you can find titles of painting and drawings that do not take away from the viewing experience but that either clarify or enhance what you are looking at. A fantastical drawing (9) that looks like part princess, part twin birds is listed as Exquisite Corpse; it helps to know that this drawing was done as a game and was composed by four artists. You can still enjoy its oddness, even with this information. A 1940 sculpture that appears to be a head wrapped in fabric and feathers by Eileen Agar (VI) is titled Angel of Anarchy. We can feel the mood of the piece by looking at it without the title, but the title adds a new idea and gives us a fresh starting point.
A quick glance through the book yields no work titled, "Untitled." Many of the works are so mysterious that "Untitled" would make them opaque, setting up a wall between the art and the viewer. Some mystery is intriguing. It can spark feelings, moods, reactions. Too much is confusing. It is nice to be able to both feel and understand a work. (See the previous post: The Mirror Business.)
A third way a title can work doesn't necessarily hint at the subject or theme, but it builds on the concept. If on a winter's night a traveler by Italo Calvino, for instance, has a fragment for a title. The book isn't quite about a winter's night, but it is kind of about a traveler. Really, it's about fragments and writing and gathering stories and reading and the suspense that builds and what we expect from a book and on and on…
When you make a work of art (and I'm including writing as well as visual arts), consider a title. Try making lists of everything you were thinking when you created the piece. What it reminds you of. The subjects involved. The mood. How you want the reader to react. Play with the concepts and play with words. Look at words that have double meanings, particularly those that can be both nouns and verbs like "envelope" or "link." A title can distinguish, clarify, and add dimension. It is the frame and context, and can be an integral part of the creative process and of the final creative work.
A side comment:
I was more than halfway through the Calvino book when I looked more carefully at the montaged image by Shelton Walsmith on the cover. The lines are made up of lines from the novel. But you have to see this up close, and although his wonderful images have graced other Calvino books and can be seen online, this one is not on his website.