OFF definately OFF,it'll offer more spring resistance on engagement making it engage slower (slip more)
Your right mountain man, I know a guy who burned his fibers because the spring was left on. Also, I had a friend who fried his fibers on a CRF during a 2 hour harescramble. His actuator arm had mud lodged around it limiting the travel of the arm, he didn't notice it because it was a mud race and he thought the back tire was spinning, but instead it was his clutch slipping. I have never had any problems with mine, but just keep an eye on things.