I think the original question was suggesting that there are some issues with the technology. And Maybe so.
The technology works like this:
We pair our watches to our phone and enter the secondary phone number for call forwarding. When we walk away without our phone, we lose Bluetooth connection. We expect our phone to forward calls to our watch. Now its the loss of connection that sparks the question. Call forwarding is usually a manual thing. This tech relies on disconnection of Bluetooth to start the process. Firstly the phone needs to identify a few things. Did the user turn off the watch? Did the user walk away without their phone? If the watch was turned off, then that too means the Bluetooth connection is lost. But we wouldn't want the phone to start forwarding calls to a switched off device, would we? So the phone needs to check. That's why the watch, when a sim is inserted, need the data enabled. The phone remotely accesses the watch, via the internet, to check its still switched on. After the phone sees that the watch is in fact turned on, it will then change its call forwarding properties to forward calls. This takes a short time as well as relying on a reasonable network connection. That's perhaps why it can sometimes fail. If we turned our watch off, the phone wont be able to reach the watch and the phone won't change its call forwarding properties. I expect Samsung might try to solve the lag time in changing the call forwarding properties, but this does heavily rely on the network connection so it might be a tough one to solve completely.