The Valley of Ashes is a monstrous junk dump. The spoiling valley speaks to the decaying American dream. Tom, Daisy, and Jordan, with their unlimited socials and shallow lives speak to how material overabundance decays their extremely souls. Their lives, similar to the valley, are empty. Over the long haul the valley gets ranker as do the lives of many characters in the novel. Narcissistic people litter the story with inane "junk", much like the valley itself.
The narrator's point of view allows the reader to develop a better understanding of the author's opinion. The narrator's point of view allows the reader to understand the perspectives of all of the characters.