I only have the comment box enabled on fairly recent Hubs. It probably doesn't do much for my traffic, but I want to moderate all comments, and I generally aim to reply to all of them. I want to moderate them all mainly because I don't want someone having a big spam-fest/link-fest without my noticing; and I like to reply because I sincerely appreciate people's taking the time to add their thoughts on a subject. BUT, because I've been on HP for quite awhile, and because this is a spare-/skimmed- time thing for me, I'm not really able to keep "getting called back" to Hubs that are - like - four years old. Also, I was finding that the ones that consistently got the most comments were the serious ones about things like grief, so they deserved real care in a reply. Because of that kind of subject, too, I just got so that I didn't want to wake up in the morning, check my comments, and "get called back" to some depressing Hub that I'd written in an attempt to help someone; but that had enough personal involvement for me that I did find "keeping visiting" it kind of unhealthy for me to do.
Contrary to popular belief, sometimes not having a comment capsule is not because the writer doesn't care what any readers have to say - but, instead, because s/he cares a lot. but may have to streamline some of his/her time spent on this site. :) (I pretty much approve anything clean and in keeping with HP's/Google's TOS, so opposing viewpoints aren't an issue for me. Believe me, though, if one leaves comments set to not require moderation, it's only a matter of time before a big spam fest to some questionable site happens. :/
I leave comment boxes on for a few months (and much of the time nobody comments anyway). Then I disable them either completely, or so that no additional comments can be added. I'm not really comfortable doing that all the time, but I had - like - 350 Hubs at one time. Replying to comments was turning into a "full-time job". :/