Good writing must show the audience what the author is trying to say rather than merely telling. In prose writing such as short stories, novels, narrative essays, and other writings, the author frequently has time to "show" the audience by using vivid language and strong words. Poetry is sometimes much shorter. It is also frequently restricted by a particular format, rhyme scheme, meter, and etc. Thus figurative language enables and author to pack a more powerful punch into a smaller amount of wording. Consider the following:
The harsh words of the father wounded the young daughters confidence, and she soon found tears pouring down her face despite her best efforts to remain stoic.
If this were prose it would work.
For poetry you might write it like this:
The lashing of her fathers words
ripped at her confidence
and opened a hole in her soul
Poetry appeals to the heart as prose appeals to the mind. The poet uses figures of speech to extend the literal sense of a word so that it affects the emotions and feelings of the reader. Most often, poetry expresses a personal concern or a serious observation which must be given due care and attention. If these things are overtly expressed, they won't have the desired effect on a reader. A critical response from the reader can be elicited only when he is subjected to deep contemplation through the use of figurative language.