Sometimes when I check in at a hotel I am asked to drop the key at the reception before leaving the premises, even if I will stay longer. When this happens, I normally do like they ask me, but sometimes I forget and take the key with me the whole day. Even then, when I come back to the hotel in the evening I find my room cleaned and nothing different happens.
So why do some hotels ask you to always leave the key at the reception before you go out? This seems like a waste of time for both the reception and the guest, so I imagine there must be some advantage?