Should you avoid introducing characters that talk one time and never talk again? I wrote a scene in a chapter where the main characters talks to a technician, and then the technician is never seen again, and I am not sure if I should remove it, because the scene gives a lot of information about the world and the technology used, so I am wondering if I should remove the character and if there's a better way to give out detailed information about the world.
Based on your description, while the technician is not pivotal the story, the main characters' interaction with the technician is important. This new information about the technology and the world informs your readers. I would only have concern if there is an in-depth back story of the technician that does not tell the readers anything about class, culture, or life experiences. Then it would be "irrelevant". However, using other characters through a question and answer format to explain the world is a very common technique to organically introduce your readers to new information.
Who says one off characters aren't relative to the story?
Say you have a story where the main character is the head of a company. Several hundred people work for this guy - you're not going to introduce all 351 employees in your story. You might have a handful of characters who routinely interact with your main character - these will be fleshed out characters that your readers know.
Now your main character comes in on a weekend to do some paper work (or whatever it is bosses do when they show at work on a Saturday morning) and runs into one of the employees doing some overtime.
You have several options:
- Boss says "Good morning," then pretty much ignores the employee.
- Boss addresses the employee by name, and stops for a chat that involves knowledge about the employee and their current position and tasks, then suggests the employee not stay too long because every body needs time to relax on the weekends.
- Boss doesn't recognize the employee, asks what the person is doing in the building, then throws a fit and sends the employee home because he (the boss) didn't authorize overtime for the employee's department.
The employee isn't important. What's important is how the boss interacts with the employee. This random encounter with a tertiary character is a chance to demonstrate what kind of person the boss is.
- Busy but polite.
- Interested in and knowledgeable about his employees and takes time to see how they are doing.
- Something of a jerk, or alternatively the company has financial problems and the boss is in a bad mood.
Make the Scene Work Harder, or Cut it
You can absolutely introduce a character for one scene. The real question is whether the scene is worthwhile as it is.
You describe the scene as if all it does is world-building. I would either expand it or cut it. Scenes need to do multiple things at once.
The most important thing I scene needs to do is provide a source of tension. Meeting the technician should have some risk.
Maybe the MC needs to convince the technician to do something, or the technician is trying to stop the MC from moving forward, etc. Without some kind of stakes, the scene will feel unsatisfying no matter how useful the world-building section is.
If the scene is unsatisfying: either cut it, or add to it until it is interesting.