Right now, I'm tired and happy, because I'm working on a production of Romeo and Juliet. I got cast as Pretuchio (no, I'm not confused about what play I'm talking about. There's actually someone with that name in this play, too) who has one line. Teensy part, but I was willing to do it, because I wanted to be in the play.
Petruchio turned into Nonspecific Extra. Being a nonspecific extra can teach you about character development. After all, how does one convey the difference between Guy In Background Who Got Stabbed and Guy At Dance? However, that's a subject for a different time.
The show is tonight, and due to a virulent rumor that I have the play memorized (I don't. Do I look like a crazy savant to you? No, I'm not.) when one of the other extras got the flu, the director asked me to take over his lines. I got this news on Wednesday.
How does this relate to writing? Well, this got me to thinking, How interchangeable are the folks in the background, anyway?
No one would dare suggest replacing Romeo was a guy from the background, or even using Mercutio and getting everyone else to move up one. You do not shuffle leads like that. But extras get shuffled around all the time.
All stories are full of extras. That person your MC bumped into on the way down the stairs is probably an extra. The waitress who sold MC a cup of coffee on her way to school is an extra. These people might get a few lines and some description devoted to them, but they are, for all intents and purposes, extras.
So, how much do you need them? Or, how much of what makes them them do you need? If I told you that you had to cut three of your extras, you probably could. But would the story suffer as a result. One could argue that it might. There will be less variation in the flavors of the story.
If you cut the shopkeeper with the Scottish brogue, there went one interesting tidbit. If the two stamp collecting neighbors become one, you might be losing some interesting/comedic/quirky dialogue. If every time the character goes out, they always run into the same person in the hallway for their gossip, the reader is going to get only the tiniest glimpse of the people who surround the character.
Just because you've simplified the picture doesn't mean that it became a more interesting one to look at.
Moreover, since no two characters are, or should be, the same, one could say that they won't fill the same role the same way. Though they could get the same job done, pass on the same info, they won't do it in the same way.
For example, if the girl downstairs in the MC's building is strangled, the kindly old man who lives next to the neighbor might say that it's such a shame that she's dead, that she was such a nice girl. A persnickety, religious 60-year-old woman, on the other hand, might say that she was a sweet girl sometimes but deserved what she got for having such a parade of strange men in and out of her apartment all the time. These could both be reasonably accurate (skewed by character's perspective of life, but mostly true) descriptions, and they would both pass on that the girl was dead, but they aren't the same, are they? What if the reader didn't know yet that the girl had a lot of gentlemen callers, and the reader needed to know. Then the speaker would need to mention that, so you would need the kind of extra who would fill the role that way.
How do you feel about swapping in the extras? When has simplification gone too far?