Arbitrage - especially given that it is a value that is guaranteed to have differences on a day cycle.

https://www.utilitydive.com/news/utility-scale-battery-stora...

https://www.ny-engineers.com/blog/two-ways-to-use-grid-tied-...

Things like https://www.hawaiianelectric.com/products-and-services/custo... note the https://www.hawaiianelectric.com/products-and-services/custo... - the CGS Plus and Smart Export involve use of a battery that isn't necessarily home power sufficient.