I agree, especially if you want to normalise or temper a piece of steel when you really need it to cool as slowly as possible. The old trick is to bury it in broken pieces of brick and heat the whole lot up till the steel is red hot. The bricks let it cool at a sufficiently slow rate to have the desired effect.
I do take on board the point about not making a whole hearth of them though, maby that is not such a bright idea after all.