To what extent should you include tech, or magic, in a story? (Assuming you're telling a fantasy or science fiction story, where these things are a feature of the genre.) Magic and tech are the black boxes of genre fiction: your character puts something in, something else comes out, and you ask the reader to trust you that what happens in the middle makes sense. But do you need to put a communicator in every ensign's hand, or a wizard in every woods?

I've been wrestling with whether, and how, to add futuristic tech to a dieselpunk story. The main conflict comes with its own tech, so that's a given, but I was trying to decide to what extent to add other things (self-driving cars, sideways elevators, that kind of thing) to make sure the story has the kind of feel that readers of the genre rightly expect.

I was going to tell the story without added bells and whistles, and see how it worked. Then I began to realize that there are places where my characters can do their jobs better, and get to the action faster, if they have access to certain tools. So, suddenly, it's all falling into place. How would my characters do this thing? Ah, I'll invent a piece of tech for that!

The best reason to put a black box in your story is because it offers a way for the characters to do something they absolutely need to do, without being so useful that it robs the story of effort. The story, the interaction of characters to accomplish a difficult goal, has to come first. Magic (or tech) has to be in service of the characters, and not the other way around.