You can go through a very long career on the bench and never handle a case with an insanity defense. Most of those types of cases fall into two categories: everyone agrees the defense applies and there is a short, virtually stipulated, court trial or a jury trial where most but not all defendants lose. See this article by By Garrett Epps. THE ATLANTIC.
The U.S. Supreme Court recently heard argument in a Kansas case that will help refine how far states can continue to go to restrict use of the age-old defense.