Most of the time it's not a big enough deal to do anything about. This case is as good a example as any. Yeah, the comment is mostly pointless, but it's not rude, offensive, or really badly written to the point I'd go out of my way to get rid of it.
Let's keep this in perspective. Dave's well written, complete, and straight forward answer still stands, and anyone looking at this Q+A later will read that first. So it's a little more disk space, screen space, and noise at the bottom, but that's about it.
I've seen far worse comments. Sometimes people seem to chime in only because someone else wrote the answer they would have before they got there. That might be what happened here. Sometimes, someone is having a bad day and just wants to be contrary. That exchange actually started with the first comment saying the post was "staggeringly wrong", which was later edited to "I disagree". When you get a bunch of rep, your posts seem to attract wannabes that look for any excuse to find something wrong so that they can look smart. The technical vigalance is good, but the resulting comment chain is often messy noise.
So on a scale of 0-10, I'd say this one ranks about ½.
Here is another example of a completely pointless comment. We really don't care what this guy "read somewhere", and otherwise seems to be just "Looky me world!" without any relevant information. However, it's not worth doing anything about. I could reply with "... and your point is?" but that would be adding more noise.