Usually so you can control the devices from your smartphone. Phone talks to hub over local wi-fi, hub talks to devices over Zigbee. They might have a web interf

Usually so you can control the devices from your smartphone. Phone talks to hub over local wi-fi, hub talks to devices over Zigbee. They might have a web interface where you can program schedules for the lights, define "scenes" and such. So it's not entirely pointless. There is however no reason why the hub should have internet access though.