I recently helped someone who was researching for a book. We worked through a lot of old photos (35mm film) and in several cases found information that was valuable, not regarding the main subject, but often background details that were invaluable to our research. Often the act of recording a scene, particularly a street or city view, can provide a historic archive for future reference. I've made it a point to sometimes record mundane scenes of everyday life, knowing that in years to come these will become historic reference points.
Storage is cheap these days, think carefully before you discard anything. You can never be certain how useful what you have may become.
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Photographers feel guilty that all they do for a living is press a button. - Andy Warhol