The best thing I read about comboxes recently is by Ed Peters, a Canon Lawyer:
"…Third—and mind, this comes from someone who often posts in others’ comboxes!—I find that combox discussions never really resolve anything; they are effectively interminable in that, no matter how thoroughly one might have answered a question or addressed an issue, there will always be one more bloke out there able to reword the matter in such a way as to suggest that it has not yet been adequately aired. And that is not counting the people who post as brand-new questions things that were expressly dealt with just a few posts higher up! Sheesh! Anyway, I grant that this could just be the lawyer in me talking, but I like it when judges rule (usually correctly) that X is irrelevant so drop it, or that Y has been asked-and-answered so move on, or that the burden of proof in case Z has been satisfied so the matter is closed. No one really performs that kind of service in any combox I've yet seen. Perhaps no one can."
More importantly, perhaps, keeping comments closed on my posts keeps me from sensationalism or exhibitionism.
In few, it keeps me honest. I have to assume that noone is *actually* reading this, and at the same time, that someone *could*, so that I will not compromise the integrity of the enterprise, and so that I will carry out the enterprise, which is to collect the gold and jewels with which our world is littered, if only we stoop to pick them up!