Bare URLs used as article references (citations) are subject to link rot. The usability of a bare URL depends entirely on the target WWW site retaining its chosen site structure, which it is under no obligation to do.
A full citation, in contrast, gives the author, title, publisher, publication, and date of the work. So, if the web site address changes, the additional information may assist in finding the new location. If the source is no longer available on the internet, then the additional information may assist in tracking down the source if it is in printed form, microfiche archives, article/paper collections, published as books, and the like. Fully dressed citations may be filled in manually, or there are semi-automated tools online, such as: reFILL (can be installed as a Toolbox link or as a Bookmarklet), or Yadkard. For Google Books, try the: Wikipedia Citation Tool for Google Books.
