For example, I love being able to switch off the living room's lights, as well as all adjacent rooms' lights, all with two taps on my iPhone, without getting up from the couch. Also nice is turning the lights on/off at certain hours of the day, or when certain triggers occur.
My setup goes: ZWave wall switch <-> (Raspberry Pi) [ZWave hub <-> Mqtt <-> Homebridge] <-> AppleTV (Home Hub) <-> iPhone. Despite all of the moving parts, this has been 100% reliable for me with near-zero latency. It even works well when I'm away from home (albeit with a tenfold increase in latency)
Unfortunately, this setup is not a low/no configuration one, so it's not a solution for the vast majority of people, and is why internet connected IoT (Nest/Alexa/Hue/Insteon) are as popular as they are.