I’ve seen this advice before, or rolled up kitchen towels. Apart from increased surface area, I don’t really see the point. Why do you think this is a better method than just a pan of water?
The new KitchenAid model I’m considering has a built in rack at the bottom intended to be filled with water to provide steam. It’s not cheap, but I’ve seen much more expensive too 
KFID500ESS | KitchenAid
With me, its how much money I have to spend
I found one with a center grill/griddle I guess. That is what I liked. Husband and his occasional big breakfasts. It works well for a warmer.
Its nice to have a new one.
Its black! GE I think but I could be wrong
Heat retention and surface area to transfer the heat from the stones to the water and cause it to turn to steam. A pan alone only has the ability to heat a certain amount. The lava rocks add to that capacity.
My pan (and quarry tiles on the shelves) live in the oven 24/7. I like the additional mass which reduces the temperature swings when the door is opened and provides additional mass and heat transfer to the bottom of the loaves which are placed directly on them. I bought a case from Home Depot, and when one chips/breaks, I just replace it and discard the old one.
We have a convection oven / microwave combo above our stovetop. Great for holidays where the stuff that cooks or heats up fine in the convection oven isn’t taking up space in the regular oven.
Update: my new friend was installed two days ago. We got the Bosch with induction top and convection oven. So far I’ve made:
So far so good! But so much for my diet…
I haven’t made anything yet requiring a hard sear, so that’s probably on my list for this week. My big steel saute pan fits on the biggest element perfectly, and boils a cup of water in about 1 minute. Cleaning up is so quick and easy without those dumb hot coils.