I've told of it somewhere before, but a guy who was at College with me in '05 fell two weeks after finishing the course. He finished, he did not pass, could not reach the competency standard for climbing and operations with a chainsaw.
He unclipped one system, threw it up and over for the next set of climbing...but did not re-attach before undoing his lanyard... undid it, leaned back and fell...40' down, shattered ankles head injuries...never found out what happened long term.
I always put weight into the re-attached system before unclipping the other one.
I've heard of close calls with the top rope when coming down dismantling a trunk...that one is seared into my brain, gives me the heebies reading that someone actually did it! A guy on AS posted of a close call with that oh, about three years ago, never forgot it.