Igneous Additions gives you more options for each of the various rock blocks in Minecraft. So blocks like Prismarine, Obsidian, and Granite can all be crafted into various aesthetic blocks like crafting tables and furnaces.
Or walls and pillars.
And even slabs and stairs.
So now you have many more options for mixing and matching blocks with whatever fits your environments. There are even some higher powered swords made with these blocks as well.
And as an added bonus you can now make portals in any size you want!