I have recently found instances of moderators closing questions (which of course occurs with their single vote) instead of leaving them to be judged by the community in the review queues. For example :
- How to calculate work done when movement is not in the direction of the force?
- Forces behind pulling two sheets of glass separated by a thin layer of water
In my opinion these questions are not blatantly off-topic - they might be off-topic but they are not blatantly so - nor are they likely to disrupt the community, as required by the guidance for moderators in the help center. I do not see any necessity for moderator intervention here, depriving the OP of the benefit of his/her question being judged by a cross-section of his/her peers, rather than a single user, however eminent.
Moderators are human exception handlers, there to deal with those exceptional conditions that could otherwise disrupt the community.
...A lot of the moderation work is mundane: deleting obvious spam, closing blatantly off-topic questions, and culling some of the worst-rated posts on the site. The ideal moderator does as little as possible, but those little actions may be powerful, visible, and highly concentrated.
This description reflects the StackOverflow blog post A Theory of Moderation which states that:
Moderators are ... there to deal with those (hopefully rare) exceptional conditions that should not normally happen, but when they do, they can bring your entire community to a screaming halt -- if you don't have human exception handling in place.
The help center also says that
Closing is a democratic voting process where the community identifies questions that duplicate existing content, are unreasonable to answer in their current state, or do not belong on the site.
(emphasis added) David Z has pointed out to me that the help center does not say that Moderators cannot use their unilateral vote to close questions routinely, but I think it does give a clear impression that that privilege is intended for the exceptional rather than the routine.
David's question Community, help us close questions! acknowledges that closure should be a community decision. It indicates that the practice of routine closure by moderators developed when there was a shortage of reviewers, but this surely is not the case today.
- What guidelines should moderators use to decide when to close questions?
- Can we please let the community close questions?
I appreciate that the review queue for close votes might grow alarmingly large at times, but I do not think moderator intervention is the correct way to deal with such a problem. If moderators think the review queue is too slow, or the system is not working, the situation ought to be discussed on Meta (eg David's 2012 call for reviewers to use their votes).
I also appreciate that questions closed unilaterally by a moderator can be reopened by voting. However, that is also a slow process, and it is much less likely to happen than it being closed by reviewers, because there is an inherent bias towards leaving a question closed, especially if it has not been improved since being closed.
My view is that the moderator's unilateral close vote should be reserved for exceptional cases, not those which are routine.