Without a doubt, there are times that using poetry to convey sentiment is much more effective than using prose.
Poetry allows more emphasis on the feelings and thoughts behind the words that could be lost if simply written out as prose. Poetry presents the emotions and speaks to the senses of the reader (or listener). By using poetry a writer can allow himself more freedom from the tight strictures of prose, even though both prose and poetry can portray the same message.
With prose, there seems to be a greater chance that the message that the writer is speaking of can get lost. Poetry stands out due to the style or format, allowing for emphasis if necessary. There are entire stories and books written in poetry format that allows the writer to tell a story in what is usually perceived as a prose format. The works of author Sonia Sones are good examples of how poetry can be juxtaposed into a traditional prose format.