A TrackBack is "one of three types of linkbacks, methods for Web authors to request notification when somebody links to one of their documents. This enables authors to keep track of who is linking, and so referring, to their articles. Some weblog software programs, such as Wordpress, Drupal and Movable Type, support automatic pingbacks where all the links in a published article can be pinged when the article is published. The term is used colloquially for any kind of linkback."
A TrackBack/linkback/pingback is important to a blogger if he or she wants to know if other blogs and sites are linking to his or her blog and who those other blogs and sites are.
Some blogging software will ask if you want to participate in trackback. You should say yes, in case you're ever curious about how people are relating to your work on the Internet.
How Trackback Works, cruftbox.com
TrackBack Development, MoveableType