>Why another screen?

One of the motivations is to have a "master controller and dashboard" for the (smart-) home that's conveniently always attached and connected to the house itself.

Consider that many houses already have wall-mounted control panels in the main hallway or kitchen for the burglar alarm or thermostat. Replace that with an all-in-one smarthome touchscreen that configures the same security system as well as everything else ... HVAC, lights, blinds, door cam video feed, etc.

Examples of that concept from other home automation companies such as Crestron, Savant, Control4, etc:

https://www.google.com/search?q=Crestron+home+touchscreen+ho...

https://www.google.com/search?q=Savant+touchscreen+home&tbm=...

https://www.google.com/search?q=Control4+touchscreen+home&tb...

Apple's product marketing pages for HomeView at the moment don't heavily promote the idea of customized programming for home automations (HomeKit API) to compete with Crestron/Savant but many observers think Apple wants to expand into that space. (https://www.apple.com/home-app/)

A lot of homeowners don't want to be locked in with Crestron/Savant. Yes, Apple is itself also a "walled garden" but it's a more palatable lock-in situation than the ridiculous re-programming fees that Crestron dealers charge for every little change.