The same thing happens in the theater world. There are the lead characters whose plights the plot is built around. Then there are secondary characters who may or may not play a crucial role in moving the plot along, but do many other important things. For a stage production, a scene or song for one of these secondary characters might provide time for a needed costume change for other characters, or a set change, or most often the comic relief. Some stories that have lead characters who get themselves into terrible trouble or bad things just happen to, well it's good to have comic relief to cut the tension.
I was cast as Meg Brockie, definitely a second fiddle character, and a sort of floozy charmer that had no redeeming features. However, she gets to sing two very funny songs. She was indeed the comic relief. "Brigadoon" is a fantasy fairy tale that if played too seriously can be very hard to swallow indeed. Meg's character helps keep the show lighthearted and funny.
The 1954 movie "Brigadoon" starring Gene Kelly, Cyd Charisse, and Van Johnson in some respects is quite depressing. Van Johnson's character is rather jaded and cynical and Gene Kelly's character is trying to run away from his intense New York City life. Cyd Charisse' character is bemoaning the fact that her younger sister is getting married, but she is not. And there are other characters that are dangerously angry. Pretty grim when you think about it.
As one would expect, the dancing plays a supremely important role in this movie version of the storytelling. And being a movie, there was no need for certain songs and scenes to cover for set changes or costume changes. But they really could have used Meg's songs for comic relief. Because the story-line of the movie is quite sad, I really missed "The Real Love of My Life" and "My Mother's Weddin' Day" (Meg's songs that were not included in the movie).
This is an example of how a "second fiddle" character was nearly completely removed so that the lead characters would get more time to expand their dancing roles. However, in my opinion, the storytelling in the movie "Brigadoon" suffered for it.
Let's hear it for the second fiddles who really play a first rate part and should be celebrated NOT CUT!