You are welcome! My very small contribution to the system (I asked and "pushed" for it) - of course, Dang and/or his team implemented it. It is pleasant to read about it in such appreciative terms.
[-] collapses the replies so that you can easily see what's next. On reddit the equivalent functionality is a button literally called "hide child comments."
But as another comment mentioned, you can click root | parent | prev | next to get navigated through the thread. Personally, I prefer the collapse, though, as having the top of my screen move without my direct control is a bit jarring, but there's more functionality from these buttons.
Important fact:
The [-] does not remove a point. After you get 500 points, you earn the privilege of down voting, you will get a "down triangle" underneath the "up vote up triangle" that you can click on.
(Also is this relavant or am I just piggy-backing your top comment?)