Is energy density required for all applications? Something that's not desirable for say a car doesn't mean something isn't good enough for say non-mobile applications.
Well, yes actually. If you're talking any kind of batteries above Duracell level, then it's important to understand how much power can be stored in a given "unit"
Of course you need to know the power per unit to some degree, but when you're building warehouse-sized stationary storage arrays, land is cheap and LCOS is more important than energy density. That's a very different tradeoff calculation than if you're building a car.