The permalink is a clickable field that is available for users to click to save a particular blog entry.
The permalink is used to "save" the location of each specific blog entry. Any of your members that want to save a particular blog entry would click on the permalink so they will be able to return to the blog entry that they want as opposed to a blog entry that may have been copied over it.
The permalink is also used by the rss feed to be able to get to the blog entry as well. When editing a blog make sure the full url to the department or content page of the blog is filled in the form field asking for the blog url.