There's a good account of using imagery in the CIPD's Coaching at Work magazine: 'Picture Perfect', written by Eve Turner.
As Turner explains,
"Imagery, including metaphors, is a normal part of language. Phrases like 'I feel fit as a fiddle' or 'It's raining cats and dogs'" are commonplace."
Turner explains that in psychotherapy:
"Imagery is seen as the language of the unconscious, a key that unlocks the link between our conscious state (our present) and the unconscious / super-conscious. Many writers believe thinking in pictures achieves a closer representation of people's inner reality or unconscious processes than words."
I think this true and has utility in a consulting or HR partnering context as well as in coaching.