I'm assuming this setting stops towers from being made from emerald blocks etc? but i turn it off and it doesn't seem to do anything. as far as I'm aware i don't have anything altering roguelikes at all.
using 1.12.2 1.8.0 version. thanks

oh right. i have random and precious blocks both set to false so not sure whats happening

At the moment all it does is prevent diamond/gold blocks from spawning on the nether floor.

If you've changed the configuration to use the setting "random=true" then you will get bizarre structures made out of diamond blocks either way. It's meant as a joke setting.