Techniques can draw attention to a specific phrase, emphasise, create atmosphere, personify.. they don't just tell the story, they are the backbone of why the song/poem is successful. Techniques aid our understanding of a poem or song by pointing out the most important or relevant parts, or by leading us via metre or rhythm to a conclusion.
For example, alliteration / onomatopoeia in 'the softly hissing snake' creates an image of the snake and almost sets us on edge when we read it. It creates atmosphere, or adds to the atmosphere. This helps our imagination grasp the images presented in the poem.
In songs, you want to look at things like assonance and alliteration which add to the rhythm of the song and aid the flow of the story. Repetition adds emphasis to sections. Metaphors and similes aid our understanding of perhaps immaterial objects like love, hate, fear.
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