When I mouse over the downvote button of a question, I see this:
This question does not show any research effort; it is unclear or not useful.
However, there is also a flag for unclear questions (at least in SO) with the following description:
unclear what you're asking
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.
My question is:
What's the difference and, thus, which option to choose?