Questions where there isn't a clear-cut answer, but a range of opinions. For example, questions about whether one should do something, rather than whether one can do something according to halacha.
The FAQ list says, in part:
To prevent your question from being flagged and possibly removed, avoid asking subjective questions where …
- every answer is equally valid: “What’s your favorite ______?”
And, indeed, a standard closure reason for questions is:
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or specific expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, see the FAQ for guidance.
As it says, though, this applies only to subjective questions. If I find a question worded as "what should one do", I'd normally assume it means to ask the objective question "what does God want one to do, as far as we know via authoritative interpreters of His will" (though it should certainly be reworded to make that clear).