I recently went to a couple of lectures on psychoanalysis in literature. The guy giving the lecture was a practising psychoanalyst and also a professor of literature. I don't remember his exact words, but he mentioned something about readers subconsciously projecting their own fantasies onto a given text, making reading subjective.

I really like the Adam Phillips quote...I personally tend to find "useful" anything that is moving, or meaningful or laden with something that intrigues me. I also think that the terms "useful" and "true" are subjective and malleable based on our inner thoughts and feelings. The human mind is like poetry...we often tend to dig deeply for meaning and in that sense, psychoanalysis can't be an exact science. You can't try to make sense of something fluid and oblique using sharp and rigid tools.