It's a tool for bloggers. I'm actually thinking about disabling it because it may confuse first time posters or users on our forum.
There's a really good explanation here of how it works, I'll quote key elements...
Let's say you're reading a blog and what they had to say spurred you on an inspiring and even exciting new train of thought. Rather than clutter up someone else's comments section with a long post, you can post your entry on your own blog. Using the trackback feature, if the blog site supports it, you can take the Trackback URL, usually a link below the blog entry you read, from the site and put it in the Trackback URL blank on your blog.
Your blog site (HSB in this case) takes the URL and trades information with the other person's blog. Your site tells their site that you have a posting related to theirs and tells it to list it as a trackback on the original post that inspired you.
Then I put that on my blog along with my take on the subject. Now at this point this is no different than just providing a link to another site that inspired you to write on your own blog.
Now unless the blog or site you grabbed the link back or trackback supports automatic what I will call "reverse trackbacking" then on the original site there is no reference to you posting something on your site. Is that right? Won't it be just as easy to leave link to your blog post on the original site? And put a link to the original article on your site?
Where is the advantage if you can't be sure the original site does "reverse trackbacking"?
If they do reverse backtracking, then by all means do it, but spammers just used it to bypass my measures, so I simply do my two-way links manually by them posting comments on my site, and I post on theirs. Simple