This way you're not stuck with a useless home in case your controller lost power, is down for maintenance or whatever.
For light switches I use Z-Wave modules that use the wall switch as a low voltage switch to trigger the module to switch the A/C circuit. This way the existing switch acts just as it did before. My family really doesn't notice, yet somehow that porch light is always on around dusk and off by dawn.
I don't use Alexa or the like but as a developer I easily integrate with DiY equivalent.
That last point is probably a key gap generally though -- as a developer this home automation stuff comes easier to me, potentially.
Combability wildly varies between manufacturers, you have have to know what works with what.
The mesh capabilities are kinda wonky, where you have some kind of "heal" network function you use when devices for some reason stops talking to each other.
"Press the button for 3 seconds, but not five."
"Do the pairing near the receiver."
And you have to swap batteries.
Being able to say "Hey Siri, good evening" to switch to my evening scene, or "Alexa, turn on the lights" to turn on the lights in whatever room I'm in becomes a huge convenience, not a novelty.