IMO, it depends on the context. what is the justification to close it.
If it really is something obvious and non-contestable that it doesn't belong, then I don't mind stepping in to close it early. However, if it is subjective and the user simply wants it closed, I'll instead wipe the moderator flag and move on.
As an illustration, a few minutes ago I went through the SO flags; I only acted on about half of them - the half that were actual, real problems.
If the numbers got big, maybe we'd need some kind of internal moderation rep counter... i.e. does the user have a history of casting bad moderator flags ("crying wolf"). Then, maybe that isn't a great idea... I don't know.