Symbolism, Imagery, Allegory
Bartleby lives in his office. This isn't a metaphor or an exaggeration; the lawyer who owns the offices discovers that Bartleby literally sleeps, eats, and spends all his time in the office. When the lawyer comes to his office one Sunday morning he finds Bartleby "in his shirt sleeves, and otherwise in a strangely tattered deshabille." (2.88) In other words, he's not dressed. How embarrassing.
So why is Bartleby sleeping in the office 24/7? He appears to be homeless—but what's interesting is that everyone else appears to be homeless too. Or at least, you never really see any of the other office inhabitants anywhere other than the office. Turkey and Nippers and Ginger Nut; as far as the story is concerned, their lives begin and end in that office. They may (unlike Barletby) have lives outside, and they sometimes mention those lives, but you only see them at their desks, copying more or less effectively. Even the lawyer narrator—he mentions that he has a home, but what happens there is blurry and unimportant compared to his relationship with Bartleby.
"Bartleby" creates a world in which the office is everything. You work and you work, and you sleep still working and you wake up still working. It's a vision of existence as an endless white collar job. Work at home was receding into the past when Melville was writing; more and more "work" meant what "work" means now—spending your life somewhere away from those you love, making money, and picking up your real life only in the evenings and on weekends. The office is everything, which means workers are totally disconnected and alienated from their own lives. No wonder Bartleby prefers not to; as a creature of the office, his existence already feels to him like a dead letter, sent out and never delivered.