Whole house is already HomeKit, is there a real reason to move to Home Assistant rather than just running Homebridge

I run both and it is not really a choice between them. Home Assistant does the logic and talks to the odd devices, then exposes what the family needs back into the Home app, so my partner still says the same things to Siri and never knows anything changed. Homebridge on its own is a bridge, not an automation engine, so the moment your rules need forecast data or a proper state machine you will outgrow it. Keep HomeKit as the front door and put the brain behind it.

Politely disagreeing with the top answer, because you are describing exactly one broken sensor and one automation you cannot write. Buy a sensor that speaks HomeKit natively and write the heating rule as two simpler automations, and you are done in an evening instead of adopting a hobby. I moved to Home Assistant for the same two reasons and now I maintain an entire second system, which I like, but let us be honest about what it is.

Practical numbers from running both on the same little box: Homebridge idles at almost nothing, Home Assistant with a database and a handful of integrations wants real memory and writes to disk constantly, which killed one SD card for me. Restore time matters more than idle load though. A Home Assistant backup restores in minutes, and rebuilding a Homebridge config by hand took me most of a Sunday.

Whatever you pick, migrate one room at a time and leave the rest alone. I did the whole house in a weekend, everything worked and the family still hated me, because thirty accessories all changed names on the same day.

Homebridge to fill gaps in HomeKit. Home Assistant when the automations are the point. Running both is normal and nobody will tell you that on the product pages.