I have seen on this site that a single moderator(@goldpseudo) controls the whole site without any concern about establishing consensus and engaging the community in closing questions , ideally the community should vote to close a question , most of my own closed question were deleted and closed by this single moderator without establishing any consensus atleast from other mods. Since this is a beta site the moderator's major role is community building but taking away the responsibilities of the community and misusing the community features like "voting to close" makes the community feel that their votes are of little value.
We have the power to unilaterally close posts that need to be closed because we can't always wait for the community to do so themselves, especially with a community as undeveloped as this one.
Of the 2200-odd users on this site, barely fifty of them — four of which are moderators — are capable of casting even a single close vote. Even if there was a clear unanimous agreement among all these users that a particular question needs to be closed, it would still require enough of them being active at the same time and looking at the same post to cast sufficient votes to do anything.
And the longer one waits for this community action that may never reach critical mass, the more likely a bad question is to just attract bad answers or otherwise detract from the quality of the site. Which will, of course, deter the actual experts we're trying to attract from actually participating in the site at all, thus preventing us from building the necessary critical mass to do the community action, and so on. It is a vicious cycle.
If we had a developed community, moderators would not need to unilaterally close posts near so often. But we are not at that point yet.
So, in short, when should a moderator close questions? When he sees a question that needs to be closed. Period.