Photos
 

Back in the days of film cameras it seemed to be expensive and time consuming, buy the film then fiddle about loading it, take photos then wonder how they will turn out, spool finished and off to the chemist, wait up to a week then go and collect. If you wanted to give a copy to someone it was back to the chemist and order a copy.
At one moment in time slides instead of photos were favoured but no matter what 'film' was used there was never a great many photos or slides taken by the average family.
Over time old photos may get damaged, lost or taken by another member of family so the number is reduced even further, all my slides and some other photos I thought I had have remained hidden despite many searches.

Digital cameras with enough memory of course mean many more photos will be taken than there used to be, no chemist no waiting, just plug and play as they say - just remember to save them externally more than once.

I've commented on this (possibly elsewhere) before.
IMO we will lose 'history' as, instead of having hard copies to thumb through there will just be anonymous discs. Assuming that the technology exists to read these, I doubt that our descendants will bother to take the time to sort through to see what they contain.

While I agree digital photos or other electronic documents can easily be lost, surely we as the first generation of digital photo keepers have a duty to keep them in an up to date well marked readable format and even better we could simply 'print' copies and write on the back what the photo is. Don't forget other electronic documents that you think is important so print and store as well.
Nothing worse than finding old family photos with nothing written on them and you have no idea who the people in the photos are and the only person who could have told you used to live in the house you are now going through.

Regarding our descendants going through our discs etc - I think they will - I would.