Creating internal hyperlinks in Drupal, from one page to another, can be slightly tricky - node IDs, path aliases, the Drupal url() function, all play a role.
Fully qualified links, those that contain the entire address including http, are easy enough to use, but it's not good practice to enter a static, fully qualified URL when linking from one page or blog post to another.
Fully qualified links, by definition, include the domain name. If that changes all these links break, and, if the site is substantial, it would require a lot of work to fix everything.
Luckily there is a better way...