Who uses lava rock?

Random question more than anything.  Anyone use lava rock between the grates & RF plate (on top of the RF plate)?  Experiences with lava rock and a reverse flow?

Its for my reverse flow with propane burners (which makes it a little bit different).  All of my bbq's I've ever had I always put lava rock in underneath the grill grates (will be doing so on my latest build), above the heat source to act as heat retention & grease collection.  Also helps with the seasoning of the grill with the lava rock sucking up the grease & the burners/heat releasing that flavor back into whatever your cooking.