I've found that there are times that I do not like seeing multiple answers to the same question returned when I try a search. While I wouldn't suggest removing the default behavior, I would like to see a search option that allows me to indicate that I want only one result per question in search results.
To give a general idea of why this is desirable to me lets run through a general use case, in fact were use my current search that inspired this post, though it's only a partial example.
Lets say I have something I want to know about which is either obscure or hard to search for due to the difficulty of good search terms. In my recent case I was looking for some specifics about how various languages handled branch prediction, so I did a search on "branch prediction". In this example I probably could create a better search so it's not a perfect example, I have had other searches that were harder to narrow down in the past where I had similar complaints; but since this is the one I remember lets use it as an example for now and ignore that I could have written a better search for it.
Not liking the relevance searches I switch to search by votes, expecting a good highly ranking result will exist which does a through analysis of exactly what I want, it's a common enough question. What I get back includes a list with more then half the starting results being answers to the question: Why is it faster to process a sorted array than an unsorted array?.
When I see the first answer I open it up and jumped to the question and looked at the first few results. They were interesting but not what I needed; I'm willing to rule out this question as unlikely to give me the analysis I want, and I have already scanned through many of the top answers. Having ruled this out I would prefer not never see it again in my results, so I can focus on the results I want.
I could try filtering by question only, to never see answer responses. Again in my use-case this is pretty viable; but that isn't always the case. if I filter by question the above linked question, with it's massive votes and wonderful answers, would never show up in my results. In fact many of the highest voted questions don't show up, because the users didn't know that "branch prediction" was the answer to their problem they didn't know to include it in their question. While the above question didn't suit my needs I imagine it could have suited another, and missing out on it and related questions with wonderful answers, but which didn't use the phrase "branch prediction" in the original question, would be a lose.
What I would like to see is a way to specify that I want to see any question once in my results, be the result a question or an answer. This way I would detect answers to questions like the above where the questioner didn't know what to ask about; but I wouldn't see the same question multiple times forcing me to skip each answer to a question I ruled out as unlikely to be useful to me.
It seems this problem is less severe when you use the relevance search, the other search options are all more prone to this issue, with "votes" seeming the most likely search to have a problem with. That may mean that this comes across as too rare to be worth addressing, but I've personally run into the frustration a few time (mostly when I'm just looking for interesting Q&A to look at rather then hunting down specific answers admittedly). I don't think it would be hard to toss in a search option to avoid duplicates either. Could this be implemented?