Since I work with archives, I'll add in that you never know what will be "historically relevant". Relevance is for history to decide. I have cataloged and researched photos, and some mediocre ones, too, of locomotives where there were probably dozens of shots. And then you notice a detail or an item in the background that turns out to be very relevant to what you are researching. Often, it is not even the primary focus of the photo.

You never know.