Cerys progression largely depends on oil cracking recipes being unmodified from vanilla, and so is not compatible with mods that change this, for example ones which replace the water with steam.
This mod adds a new compat recipe to alleviate this, without affecting anything about progression within Cerys or in general - it adds a new recipe, unique to and only possible on Cerys, using the original items, plus optionally one of a couple cerys ores for additional "flavor".