Commenters tend to fall into three categories: regulars, lurkers, and sporadic. The regulars are the ones who will post on nearly any topic or post by the blogger or site, they've always got something to say and for them, its sort of community that makes them like a site than anything else.
Chris Anderson wrote a book called The Long Tail which notes that any successful business has a big, loud, and regular group of consumers but a lot of people who are quiet and consistent in their interest. The graph looks like a sweeping curve with the bulk of it off to the right, like a tail, thus the name. And commenters are like that too: a bunch of comments by a few people, then not so many comments each by a lot of others.
Lurkers tend to comment very rarely, and are there only to read. Sporadic commenters will post on occasion when they are particularly moved to make a statement, but usually are quiet. Unless its a topic they are especially knowledgeable and experienced in.
Then you hit someone's "wheelhouse" where they are very familiar with the topic and have plenty to say. Sometimes this can end up almost a question-and-answer session where the commenter/expert will post many times answering direct questions by other commenters on the topic.
I had this recently happen on an Ace of Spades HQ post on the upcoming X-Men movie Days of Future Past, which is very vaguely based on the comic story in issues 140-141 from 1980. Its a time period and series of stories that I'm quite familiar with and could help people know more about. In fact the X-Men in general, up to the early 90s when I just didn't care for the way the stories were going any more, are an area of some knowledge for me. And that includes the movies, such as who the girls are who played Kitty Pryde (Sumela Kay, Katie Stuart, and Ellen Page - for some reason, they recast her in every film). Of the three, Sumela Kay had the best look for Kitty, in my opinion.
So when this topic came up, I was ready and had plenty to say about the characters, storyline, and films, and not very much of it positive about the last two (X3 and First Class). I hope the next one is better, but I'm not confident.
A Wheelhouse Comment is one where someone is an expert and its like a hanging curve right down the middle of the plate, exactly where a batter likes to see the ball. The commenter can crush the topic out into the parking lot, as it were, with plenty of knowledge and inside information on the topic.
Often this can be quite interesting and informative. Some topics will have several Wheelhouse Commenters, such as a post about guns or the military. They can be very useful, interesting reading on the topic, providing a treasure trove of research and data on something that most people either have no time or familiarity with.
On the other hand it can become tedious. While I find the X-Men fascinating, others might think they are idiotic and childish, so extended comments on the topic could become very annoying. As a blogger at times I am concerned that I'm posting on something nobody but me cares about, but then I figure, "well its a big internet, they can always move on."
But on a blog, as a commenter, you're a guest and hence are in a sense imposing on the site so going on and on about a topic you love might actually drive readers away, which is not what, presumably, you would want if you're interested enough in the site to comment on it. So some discretion is best.
*This is part of the Profiles in Commenting Series