Add Flavor to Writing
To make a poem more interesting is perhaps the most prominent reason for using similes and metaphors. Think of a poem as food -- if there were no spices or variety of ingredients, the food would taste bland. Adding similes and metaphors, however, gives your “food” some flavor.
For a Laugh
Metaphors and similes can also be funny. For example, if you write, “He was as useful as an unsharpened pencil,” you imply that the person you’re talking about is not actually very helpful. This simile adds humor to your subject and could grab your reader’s interest.
Economy of Expression
Poems tend to express a subject or feeling in few words, many fewer than you would use in a short story or novel. According to the Purdue Online Writing Lab, metaphors and similes “give maximum meaning with a minimum of words.” For example, if all you write is a simile, such as, “My body felt like molasses,” the reader can infer the speaker feels tired or sluggish, or the audience can make other assumptions based on this short statement that might take many paragraphs to adequately describe otherwise.
On Your Toes
Metaphors and similes might also make the reader do some work -- they encourage the audience to use their imagination or even interpret words in their own way. Since metaphors and similes show rather than tell, they invite a reader to paint pictures in his mind . For example, instead of saying, “My love is pretty,” poet Robert Burns says, “O my Luve is like the melody/That’s sweetly played in tune.” The audience cannot read the simile literally, but rather they must think about what the poet means, and different readers could come up with various interpretations.
No Other Choice
Sometimes poets must use similes and metaphors because there are no other ways to express what they want to say. Or what you want to say may have been said the same way over and over, so poets must be creative to find new ways of saying the same thing. According to the Purdue Online Writing Lab, metaphors can be used as verbs, adjectives or adverbs, prepositional phrases, or appositives or modifiers, so poets have options to get inventive with their use of metaphors.