I come to gaming with skills from a lot of places. My passion for party balance comes from my experience in improv theater. In improv, one of the most important facets is focus sharing, making sure that scenes shift between participants, allowing different people to be the center of attention for different parts of a scene. This not only ensures investment on the part of all participants, but is also good for the progress of a scene. Shifts in focus allow shifts in power between character, which allows different character objectives to be resolved consecutively until the scene resolves. In the RPG, I feel that this is partially met by a sense of party balance, ensuring that shifts in narrative focus allow everyone to participate.
I've seen this done in a number of different ways. The classic version is the D&D class system, in which the four classes fill different roles within narratives and meet different challenges. Got Undead? Bring up the Cleric. Got a Trap? Bring up the Thief. This works reasonably well, but is terribly limiting in the kinds of stories that you can tell. Other systems have taken very different approaches that I find interesting. In Werewolf the apocalypse, the auspice system divides characters into social roles with the understanding that a given pack of werewolves is best served with one from each auspice, a warrior, a bard, a judge, a mystic and a trickster.
One system I find interesting comes from Mongoose's version of Traveller. In their system, at the end of character creation, depending on the kind of story that the game is going to be, the players get to divide up a suite of skills that are relevant to the story. For a game that's about piloting a ship around, you get to make sure you have a navigator, a pilot, an engineer, a sensors person, etc. It's useful, because it recognizes that these are frequent story challenges that different party members need to be able to complete. In the system, you go around the table and pick skills one by one until all the skills have been divided. It aims for minimal overlap while making sure that every challenge is meetable.
Now, while I'm a big fan of it, I don't think that respecting party balance means that you can't have some degree of overlap. I think that in systems that are open ended enough, you can engineer party balance in other ways. I've threatened to run the all bard game(and D&D5's bard mechanics make that much more possible) of D&D for quite some time. Similarity and difference can be relative between games. The most important thing is that everyone feels they have a place at the table. That there are ways to share focus that mean everyone gets to participate.
So, my experiment. The next game I run, I am going to encourage people not just to choose a character class, etc. But to actually choose a role in the TVTropes Five Man Band. Having a sense of not just how the character fits into game challenges but into the party's social roles may help. Or it may go completely off the rails. It wouldn't be an experiment if I knew exactly how it would go. But I think it's worth a try.
So, my experiment. The next game I run, I am going to encourage people not just to choose a character class, etc. But to actually choose a role in the TVTropes Five Man Band. Having a sense of not just how the character fits into game challenges but into the party's social roles may help. Or it may go completely off the rails. It wouldn't be an experiment if I knew exactly how it would go. But I think it's worth a try.