I find myself in situations when a question isn't appropriate but I know there's nowhere else for it to go, so I'm compelled to close it and yet at the same time I want to help the poster out. Other times I find I post an answer and later realize that the question wasn't really up to par.
Is it expected that people who close a question don't answer it? Should I delete my existing answer if I decide to vote to close after all?
The community does not generally react well to this practice in my experience.
For better or worse, it is viewed as a form of "nobody can answer and get reputation for this, oh except me."
You might try closing it and leaving a comment with some pointers instead.
What I'd say is not appropriate is to add an answer that is apt to contribute to the closability of the question while voting to close.
If questions that are likely to be closed attract short pointless answers, then answering with a short pointless answer and voting to close is almost like voting to close twice - especially given the fact that you cannot see who voted to close until it is closed; closing and answering is more like subterfuge in that regard.
Answering the question in a way that might help draw out the question you wished had been asked might be an appropriate way to go about things. Especially since you know what kind of stuff is acceptable here and the asker is probably ignorant of the complicated and tenuous nature of this website (and why on earth wouldn't they be?).
It depends on why you're voting to close and whether you think the community as a whole will agree or disagree but there are plenty of situations where I don't see a problem with it.
If you're absolutely certain that a question is off topic and that it's going to end up getting closed then yes, answering is bad form but I'm not sure these are the situations we're really talking about.
After all in these instances even the rep argument is pretty weak. Bad questions don't stay open long enough to get the traffic for any serious voting and if you can vote to close your rep is already high enough that why would you waste your time putting together an answer for the sake of another 20 or 30 points?
But more to the point, there are also questions I've voted to close where I've done so unsure as to whether the community as a whole will agree. That's not to say I'm wrong in my vote or lack conviction, just that I don't think the way I see it is the same way that everyone else does. As often as not in these cases the question gets a couple of close votes and stays open.
At that point not engaging with the question seems an odd thing to do, basically saying even though you think you have something useful to add you're not going to because you think that everyone else has made the wrong call.
Now if that's how you feel then fine, that's your right, but I'm guessing most people would accept the majority view and engage on that basis. After all, if whichever party we vote for loses an election, so-one suggests disengaging with the political process as a constructive or useful thing to do - you get in there and make the best of the situation.
The other thing that I'd see supporting this course of action is that whether mediocre questions go on to be useful or not often depends on the first few answers which set the tone for what follows.
If you can help steer the mood of what you see as a borderline question in the right direction with a great answer, isn't that a good thing?
I do get what Jeff says about how this can be seen, but I tend to view it that if I'm honest, helpful and consistent in the way I behave then I'm happy for the community to judge me how they will and believe that on balance they'll be fine with it.
I think its always good to answer questions regardless their ontopic or offtopic quality. After all, most of us are here to help people aren't they? Some persons are really in distress and IMHO not helping them is the real bad attitude.
So I prefer closed questions with answers than without. I've seen many yesterday.
However we should also ensure that we questions meet the community rules. I try to vote to close only on obvious problems, and I usually ignore borderline situations.
