IMO, it depends on the specific HomeKit device.
Some HomeKit devices use WiFi to communicate, so they should work anywhere in your house that has WiFi. For me, that's my garage door opener (MyQ Home Bridge), sprinkler controller (Rachio), and a few Best Buy outlet controllers.
Other HomeKit devices use Bluetooth. I think these are typically battery-powered devices like door locks, etc. I don't have any HomeKit devices that use Bluetooth.
Other HomeKit devices use their own proprietorial RF communications via a hub/bridge. An example of this are the super popular Hue lights. HomeKit talks to the Hue hub via Ethernet, and then the hub talks to the light bulbs (spread around house) using RF. Your HomeKit hub itself doesn't talk directly to the light bulbs.