Supplemental recall support for a prospective in the past.
One of the main benefits of taking a photograph is the supplemental recall support of the photographer's mental memory, of their point-of-view at the moment the snapshot was taken, as well as other sensory inputs (sounds, smells, etc) that may have been present. That's why it can be argued that taking photographs in the mirror, strengthens one's memory 100-fold. Specifically, one's ability to initiate a search of their memory- a partial index of one's memories- if you will.
