Being able to decipher the tone of a piece of writing is crucial to being able to decipher the thematic message of a text. This is absolutely true for analyzing poetry.
Love it or hate it, poetry is unavoidable in the secondary ELA classroom. I, for one, am a HUGE lover of poetry but fully acknowledge that it can be annoyingly cryptic at times. Reading poetry reminds us that not all texts are meant to be beat "with a hose to find out what [they] really mean" like in the Billy Collins poem "Introduction to Poetry."