Yes, you can use it offline. But, first you need to know its local IP address. You could find that in your router setup if you know how. Or you can use the tool we provide, which is easier. Once you know your hub's local IP address, you can disconnect the internet if you want.
The internet connection to the hub can be useful: It allows you to use our mobile app to see and control devices in your home from anywhere. You can use the mobile app for notifications, and as a personal presence device. You don't have to use these features if you don't want them. If you want to update the hub's internal software to get the latest features, it needs to connect to the internet to do this. But, this is optional. Also, if you want to use Voice Assistants such as Alexa or Google Home, these require and internet connection. But if you don't want Amazon and Google listening, by all means don't worry about those.
We have many users with hubs not connected to the internet.