I would suggest the following guidelines.
Questions that could be exhaustively answered by reference to software documentation or a technical manual should be considered outside of the scope of this site. For example:
How do I add users to a PHPBB3.0 usergroup?
Sure, someone here probably has the answer, but asking this question here would be like walking into an IEEE conference and asking someone to show you how to use your blender. It distracts from the site's focus on working with users and communities and is not the sort of question we want to encourage.
I would feel perfectly comfortable closing this as off-topic. It's not at all broad or subjective and the question is clear, but it doesn't add anything of value to this site and it's not high quality enough to warrant migration.
Here's an equally technical but more involved question:
Is there a way to animate the background image on my subreddit so that it moves when the user scrolls through the questions?
There's still a good chance that someone here can answer this question, and there are arguments to be made for hosting such questions here. Most notably, a community full of moderators is likely to include people who have used the particular system being asked about.
That being said, provided the question is neither answered nor crap, I'd be comfortable closing it as off-topic or migrating it to a site like StackOverflow or SuperUser. It's still not really about moderation or community building because the people and the community are totally irrelevant - the only thing that matters here is the equipment.
On the other hand, questions that are looking to achieve a certain outcome expressed in terms of the community or its members given the use of a particular software or system are really not about the software or the system. These are questions about working with the community and should be considered on-topic, even when they identify specific technical problems or call for technical answers; for example:
Is there a way to reward users on a vBulletin message board for being active and helpful, like the badges on Stack Exchange?
On its surface, this question could be read as request for technical help - "How can I implement badges on vBulletin?" But implementing badges is just one possible approach to the desired outcome identified in the question.
The question can easily be answered in ways that aren't specific to vBulletin but will solve the asker's problem given the constraint of having to work with vBulletin. The real question being asked is, "How do I reward users for contributing to my community?" The added context only improves the question by narrowing its scope, such that the best answers will identify a generally applicable solution along with specific instructions for applying that solution in the asker's environment.
