Is there any benefit to adding some boiling water to a preheated dutch oven (under some parchment paper) just before putting the lid back on?
Well I did it. It seems to improve oven spring. Took Some pics.
What you are doing essentially allows the bread to rise a little more before the crust toughens. It will leave you with a lighter, fluffier loaf with smaller air pockets and a softer crust. I have never poured water into the dutch oven before, but I often just wet the loaf right before putting it in. You can do that with a spray bottle or basting brush.
I'm not sure how exactly your method will differ in results though, as it will do 2 things: rapidly lower the temperature of the dutch oven (transferring the heat to the water) and start cooking the top of the loaf faster.
What does steam do for bread? Primarily, it gelatanizes the starches in the crust and keeps them that way longer. This causes the outside of the loaf to form an extended, flexible “skin.”
So, while your technique of adding the water under the parchment is novel the effect that steam can have on bread making is well established.