These papers and articles help explain why permanent URLs are particularly important in scholarly and legal citations.
"In Supreme Court Opinions, Web Links to Nowhere" by Adam Liptak, New York Times
"Perma: Scoping and Addressing the Problem of Link and Reference Rot in Legal Citations" by Jonathan Zittrain and Kendra Albert
"What If Law Journal Citations Included Digital Object Identifiers?: A Snapshot of Major Law Journals" by Benjamin J. Keele
"Something Rotten in the State of Legal Citation: The Life Span of a United States Supreme Court Citation Containing and Internet
Link (1996-201)" by Raizel Liebler and June Liebert, Yale Journal of Law and Technology