Let's say you talk about rooms and some rooms have one door, some have two, some have threes. How do you make a general statement about all the rooms without making an overly long sentence? I also don't want to use (s), because it's bad style.
For example:
The dog felt afraid in all of the rooms when Rupert made the door(s) disappear with his magic wand.
Well, you can say that Rupert made all the doors disappear, right? It sounds like there's really no need to be specific how many doors were to each room.
I can't think of an appropriate context where it would be important, but in that case you'd probably have to explain it in detail. Otherwise, default to the plural.
Each room had anywhere from one to three doors leading into it, but Rupert made them all disappear with a wave of his wand.
It breaks the flow of a narrative to specify too much detail when it's not important. This presents a challenge to the writer to put in as much detail as is necessary, but not too much.
Here's an example of what is probably too much detail. By default, I use the plural:
Some of the groups had four or more students, some two or three, and some only one student, but no matter how many students were in each group, Rupert took the time to question each separately, and ask them if they knew anything about the werewolf.
