Should you never write a subplot if it doesn't enhance the main theme and conflict of the story?

Question

Should you never write a subplot if it doesn't enhance the main theme and conflict of the story? I have this subplot I am writing and it's there just to explain the political system of the country and why different factions kill each other using assassins. The side characters disappear at the beginning of the story and reappear later on during the final portion of the story. The main theme is how war can ravage one's soul, and the main conflict of the story is against a different country. Now, the problem is that the two side characters are literally robots and there's a lot of worldbuilding that went into this, so I can't really find a way to enhance the main theme from this subplot and can't really tie it to the main conflict of the story, because the war takes place in a backward and helpless country.

So the question is should you never write a subplot if it doesn't enhance the main theme and conflict of the story?

Answer 1

I'd answer in the negative. Subplots do not have to enhance the main theme, or influence the main conflict in the story.

But your particular subplot doesn't work.

A subplot typically connects to the story fairly strongly. In Star Wars, the sexual attraction between Princess Leia and Han Solo is a subplot, so is the friendship between Han Solo and the Wookie. It reveals more to us about their characters. What it reveals may not be that important, it doesn't really affect the plot and we could do without it, but both of those relationships add color and humor, and humanizes the characters, so they aren't just utilitarian roles.

So a subplot can be there just to increase the depth of the characters, it doesn't have to create complications or play a central role in the plot.

And these subplots in Star Wars do not enhance the main theme, I don't think.

The problem with your subplot is it does not involve the main crew at all. It is not a "subplot" meaning a plot within the main plot, it is just a different story altogether. If I understand you correctly, it isn't going to add color to, or create any feelings at all about, your heroes or villains.