I think there’s a miscommunication or misunderstanding here. Let’s take the scenario where you’re going to the beach to go swimming and not bringing a bag to leave your keys in. The smart key does in fact have a detachable key blade in it, but it only locks and unlocks the drivers door. Would you be leaving the smart key in the vehicle and locking the drivers door manually (assuming single point entry is enabled). The smart key isn’t waterproof, so you can’t take it swimming.If you lock it manually with the key blade the alarm won’t be armed and if someone broke into the car, they would be able to start it since the key is still inside.
With the activity key, you lock the smart key inside the vehicle and it is disabled by the activity key. If someone breaks into the car, it won’t start. You basically just park the car, put the key in the trunk, and lock it with the activity key.