Nick uses euphemisms quite a bit in the story because he's had a genteel upbringing. He tells us on the first page that he's had "advantages" growing up. That's a euphemism for having had money as he grew up. A little later, as he's describing where he lives, Nick says he lives on the "less fashionable" of the two landforms known as East Egg and West Egg. He's being euphemistic rather than saying that he lives on the side of the bay that is where the people with less money than those who live in East Egg have. Part of Fitzgerald's style is to use long descriptive passages that sometimes employ euphemisms because the euphemisms give more of a feeling of the sophistication and privileged background that Nick and some of the other characters have. Also that style serves as a contrast to Gatsby who, though he has wealth and has worked hard to smooth some of his rough edges, still has some of those rough edges on him.