Consider the following scenario:
A (new) user asks a question that is related to a specific plugin. It may or may not employ core functionality, but is at least borderline, if not entirely, off-topic. It however is not badly phrased and does show some research effort (apart from having ignored the Tour/Help/FAQ).
Regardless, you know the answer and could help the OP without much effort or researching. It's an easy type up.
Pro for answering:
Humanity. Altruism. The want to help.
Con of answering:
It would encourage further questions of the kind, by the same or another user.
Specific example, just now: Remove All in One SEO Pack Widget while posting
The OP could have phrased the question more generic. She didn't though. She does show research effort. Also, she knows the plugin-specific part of the answer (to be precise: she knows the handle of the metabox she wants to remove and she knows how to do it). She could have asked "Why can I not remove a (!) metabox from an edit screen? What am I doing wrong?". If she had phrased it that generic, it would have been an in-scope question...
I could tell her that she's using the wrong hook. That is (or could be) plugin independent.
I left a comment to a question that should point her in the right direction. I did close vote the thing. Still, I could type up a solution quicker than asking for your opinion on meta. I however don't feel like encouraging off-topic content.
What is the right thing to do?