I often see questions marked as duplicates because they "overlap" another question. Usually, the correct answer is a part of an accepted answer on another question.
Why wouldn't we want to allow the more specific question, to help people who might be looking for the same thing? Isn't that better than forcing them to hunt through long answers for the detail they need?
Here's the situation:
Question A asks about something complicated (like, "Who is Voldemort?"), and gets an answer that answers the question comprehensively, with lots of detail on related topics.
Question B asks a more specific question about one aspect of the complicated topic (like, "Where was Voldemort born?").
Then, Question B gets closed a duplicate of Question A.
There's no doubt that the accepted answer for Question A includes the correct answer for Question B. But it's hidden inside a long answer, most of which is entirely unrelated to Question B.
Why wouldn't we want to encourage these more specific questions? Wouldn't it improve the overall quality of the site to have answers to all the "forms" a question might take?
Is there a cost to having overlapping questions that I'm not seeing?