You are thinking awfully small here. The Bluetooth range is fairly significant, I certainly would welcome the ability to 'ping' the watch from the phone in case I take it off and set it somewhere in a pile of clothes or something. Yes it would be limited range, yes it wouldn't have it's own GPS but it would be handy, especially if the watch is in do not disturb and isn't making noise with incoming alerts.
The other thing that would be helpful would be if the phone would remember where it was when the watch was disconnected. At least then you would know if you accidentally left your watch at home or if it fell off in the coffee shop.