For a rewarding role-playing game you need a deep, consistent world and the possibility of conflict, among other things. Social class helps provide both. Of course, it’s not enough just to have low-class characters. That only makes sense if there are higher classes to interact with, whether other players or NPCs.
A low-class character can be more imaginative and flexible than their social betters, because they have less to gain from sticking to society’s rules. That was my thinking when I created working-class hero Jack Ember for Mirabilis: Year of Wonders. The postwar fiction of the "Angry Young Men" was full of clever commoners like Arthur Seaton and Jim Dixon - or, even earlier, look at the examples of Kipling's "Tommy" and Twain's Huck Finn.
For an aristocratic character, strait-jacketed by social rules, it can be handy to have a commoner to take care of the grubby side of problems. Maybe the cardinal’s high-born daughter can’t countenance plain murder, however ruthless she is, but a word to her guttersnipe servant – “I hope I never see that man again” – may be enough to put her enemy in the Tiber with a wide red smile. The master-and-servant relationship is such a staple of drama that Keith Johnstone devoted more than half of his book Impro to it. Think of Blackadder and Baldrick. Wooster and Jeeves. Fogg and Passepartout. Don Quixote and Sancho Panza. Especially mature readers might even remember Mr Stabs and Luko:
Of course, servant-and-master is only going to work in an RPG if players stick to their social roles. You can’t chummily forget about status differences when it suits you. I was lucky enough to play in a campaign where Jamie was an aristocratic army officer and Patrick Brady was his sergeant. The relationship between them was pitch perfect even when (especially when) Patrick’s character was bending the letter of his orders as far as he could.
Fun though these examples from fiction and gaming are, they're all essentially romps. Yet in real life there's a heavy burden to being at the bottom of society's heap, a burden that many are overwhelmed by. Dig a bit deeper and the challenges and conflicts of being a commoner prove a lot harsher than the entertaining high jinks of Passepartout or Panza. Take a look at Mulk Raj Anand's classic novel Untouchable, an angry, desperate, tragic and ennobling account of those who are spurned as the dregs of society. Or consider the struggle of Tess of the d'Urbervilles, who suffers the double misfortune of being poor and a woman in nineteenth century England. Those are great stories to visit, but you wouldn't want to live them for real.
If you only read YA fiction you'd think that all these put-upon peasants needed was an uprising, but that's rarely an option in reality. The truth is always more interesting. Social class is hard to pull off but, like any attempt to take roleplaying seriously rather than as a make-believe send-up, it pays dividends in terms of the places it will take you.