Video game site Kotaku takes a look:
If the safety is off, or if the gun is loaded without you being aware of it, keeping your finger off the trigger will ensure that you’re using it safely. Until you are ready to fire the gun, until you are ready to destroy what you’re pointing at, you should keep your finger off the trigger. It’s far too easy to accidentally pull the trigger because of a spasm or startled response to something.
Mostly, but there’s no reason to have your finger on the trigger even if there is a safety and you “know” that it’s on.
Check out the full article over at Kotaku.
Hat tip: James