I did my conversion with Al Gwilt at MW Helicopters. He certainly covered that aspect but, even if he hadn't, securing unused harnesses is basic airmanship regardless of type. In a helicopter it's particularly important for obvious reasons.
That said, forgetting the obvious is easily done. My most embarrassing (to date) was when taking off from a friend's house in an R22 some years ago. Knowing the risk of being distracted by the group waiting for me to lift, I did my checks extra carefully. It was only as I cleared the trees at the end of their garden, and was about to tell Gatwick I'd lifted, that I noticed the heli was unusually noisy. I'd forgotten to put my headset on.
I'm sure there are pilots good enough to put a headset on whilst keeping an R22 the right way up, but I knew I wasn't one of them so it was quickly back to the lawn. :o