Check out what happens to URL when you click the # on a post anywhere in a topic.
See how it changes?
It show the specific address of THAT post. This comes in handy when you want to send someone a link to a specific post in a topics that's pages long. Instead of just sending them a link to the page (and then they have to search it out), the link will bring put THAT post to the top of the page.
And this generally works the same on all forum boards on any site.
I tried explaining this once before and got nowhere.
So I hope this explanation was a little clearer and helpful. It does come in handy.