It depends on what you mean by auto unlocking.
Auto unlock once when the device boots: There are benefits because if your device is stolen when powered off then the attacker can not copy the data offline. Without encryption, they could (even if they didn't know your login)
Always auto unlock (no matter what state the device is in, it will always unlock itself automatically for anybody and at any time): I can't think of any benefits because by definition the device is unlocked and fully accessible. I guess one benefit might be that if the device has a restricted IO/GUI/API then this prevents reverse engineering or getting at the raw data.