Eh materializing data upon mutation can bring you some gains if your product does like one thing and needs to do it very fast. But as soon as you get complex transactions with things that need to be updated in a atomic write or you want to add a new feature that needs data organized in a different way then you're in trouble.

Also deeply unsatisfied of "just slap an index on it" that was lightly trow around on the part about building an application. The index is a global state, it was just moved one step further down the layer.