It's a quite powerful tool to integrate a variety of different smart home devices into one location and share them between ecosystems.
I have a wifi thermostat that requires a dedicated app and does not allow for Apple Home integration. With Home Assistant I installed an integration for that thermostat, then shared it with the Apple Home bridge (also an integration) and quickly was able to allow my iphone/automations etc, to modify the thermostat. And that's only scratching the surface and something that took a few minutes.