Home assistant has plenty of use cases. it is not only controling devices but also a very powerful automation system. A couple of things I use it for:

-start my laundry only when I have enough solar power to power it

-notify me when my laundry is done

-track energy usage of many devices (heaters, washing and dishwashing machines, A/C,etc)

-let me know when to open or close my windows based on inside and outside temperature

-Force my water heater to turn on when I have solar power

-Expose non-homekit devices to homekit