Obsidian Entertainment's Chris Avellone has added a brief entry to his official blog that reveals his preference for implementing "a smaller, more focused" set of characters in the titles he works on. Alpha Protocol and Fallout: New Vegas - Dead Money are used as examples:
I have a question: what types of characters do you prefer? Do you like to create a mass of different episodic persons who can gave you quest, have some background story but are not related to the main hero and don't have a big role in game (like in Fallouts) or do you like to add a characters who are really important to plot and have a big relationship with the main hero (like in Alpha Protocol)? The second option equals to have a less number of NPCs, but they're deeper and cooler. Which is easier and which do you prefer?
I prefer a smaller, more focused/reactive cast (Alpha Protocol, FNV: Dead Money) to a shallow sprawling cast. It helps in the studio as well, because actors have more time to get into the character, and the results are better, imo. This worked really well with Richard Herd who played Father Elijah in Dead Money and also helped with Dog/God in the same DLC (Dave Mitchell played both halves, so he got twice as much time with the super mutant to see how the two sides balanced).
The smaller cast doesn't have to be essential to the main plot (although I'd prefer they did as long as it doesn't necessitate them being immortal or unkillable), but they do have to help the player question their own actions, support the player choices, and provide a perspective to what's going on to try and make the player think about the game conflict a bit more (ex: Cass's perspective on Caesar's Legion in FNV - she recognizes that they're basically scumbags, but not long after her quick condemnation, she goes on a detour about the good works the Legion HAS done and how crappy a job NCR is doing, which speaks for itself).