And I have no idea what the point of being able to vote individual posts within a thread is; if you don't want to read someone's post, just ignore them, why should voting up or down matter?
Two different things come to mind:
1.) On questions, the highest-rated post is highlighted as "view best answer, chosen by the community." I haven't done this, but could imagine giving a post a thumbs-down if I think it's been artificially inflated (if the poster is especially popular, for example) and another answer is in fact more informative.
2.) There are many people here who I wouldn't want to ignore in general but who occasionally
say things that I think are beyond the pale. I appreciate being able to just collapse something that makes my blood pressure rise every time I read it, rather than ignoring the poster completely.
What I said someplace else is that I like being able to kind of brace myself instead of being whapped upside the head -- if, for example, a poster I haven't ignored says something really odious and it's already voted down before I get there, I know to take a deep breath and expect something annoying before clicking "view" -- as opposed to just meandering along and then "WHOA!"