The benefits of sending trackbacks are that you are engaging in the conversation of whatever topic you are talking about. When you send a trackback and quote a popular
blog, that
blog's readers become aware of your
blog when they read the comments.
Since you are quoting or expanding on whatever the original poster is saying, you are not cluttering up their
blog by posting your thoughts on your
blog.
Finally, the
blog you send a trackback to, becomes aware of your
blog and who knows, potentially they could quote one of your
blog posts in the future.
Mark