The new method eliminates the need to contract with publishers to have official opinions produced in bound volumes (which must then be purchased), reportedly saving Illinois taxpayers hundreds of thousands of dollars a year.
As stated in the ISBA story:
The public domain citation system was first recommended by the American Association of Law Libraries in 1994 and was endorsed by the American Bar Association in 1995. Since then, about a dozen states have adopted it.
Cross-posted in Law Library Blog.