The real killer is when you want to "do something physical" in the real world on batteries, like unlock a door, etc.

That nobody has come up with a powered doorjamb instead of powered deadbolts is annoying; I'll have to build one myself using something like https://www.americanlocksets.com/hes-1006cdb-electric-smart-...

That said, I'd love an ESP32 for Zigbee. I bought an H2, but the documentation hasn't been good enough that I could make it work.