On chapter 2 paragraph 13, Ballister says that quote.
Simile and imagery
Hughes is using simile in this poem to compare what happens when you put off dreams. He compares deferred dreams to things with very strong sensory imagery like drying up "like a raisin in the sun" or stinking "like rotten meat". These details help the reader understand the heavy impact of what will happen if you put your dreams on hold.
