I'm of the opinion that our subconscious is collective, hence while out of body we can zip to anybodies location, read the minds of others whilst in the physical body and receive messages from other beings. With this in mind, it seems reasonable to me that if we offer something on the physical plane, with the right mental energy, it will appear in some capacity in the fine material realm, which to me is essentially the subconscious. So it may literally be a material gift. Of what practical use this is, I am not sure, but it may demonstrate one's devotion or commitment to a particular being or group of beings. I believe the Buddha recommends offering food to the hungry shades. I personally receive messages on a daily basis from the spiritual domain (fine material realm, astral plane, subconscious). They usually are an indication of when I should be practising samadhi. So as there is benefit in communication with the spiritual domain, I can certainly understand why others would want to perform ritualistic giving to the other side.