On average, I suggest, no more than 5% of any photograph has any immediate value to the person taking the photograph.
Look at any typical photograph, and it will most likely be of a person. That person's face typically takes up no more than 5% of the photo. It's such a familiar characteristic: photography teachers are always telling their students to "get closer" or exclaiming that "the best zoom lens is your feet!" But (a) not many people get taught to take a photo and (b) they don't usually take much notice of such advice in any case. Even if the photo is of a group, that usually means that the faces are even smaller in the frame, and thus they still add up to about 5% of the photo. As an example, look at the photograph. I don't think it's a poor photo by any means, but nevertheless, despite the rough calculations, I also don't think I'm far off in my estimations that only 5% of the photograph constitutes the key element of that photo as far as it was intended at the time.
So, 95% of the data on that photo is not regarded as important, meaningful or even interesting.
It is barely plausible, but perhaps still possible, that 95% of all photos taken are of people, the rest being pictures such as landscapes, where all of the content might be seen as meaningful. But, given the huge presence of phones carrying decent cameras within them, I suspect that people are relentlessly the 'focus' (sorry) of the picture-taking public.
But it doesn't just stop there.
People take photos of others, and then take little notice of them, and even consider discarding those that aren't meaningful or relevant enough (they don't even have 5% of importance). But it is easy to forget that the photograph will remain the same. The camera is hungry: it consumes every packet of data it sees and spews it out for the viewer. The resultant photo always contains the same data (unless it degrades). But something else changes, even if the photo doesn't: time changes.
Take a photo at Christmas at home of people in the family enjoying themselves. Look at it then, and it is a record of a few familiar faces enjoying themselves: it is a snapshot of a moment that records that event, and the event is captured by that 5% of the frame: ah look, there's Mum worn out by cooking! That's a nice one of my grandson. Now fast forward thirty years. Look at the photo again: the faces are still important, of course, but there is just as much fascination in the details within the rest of the frame of the photo too: the decor, the clothes, the colours! Look at that appalling wallpaper! What were we thinking? I LOVED that lamp!! What happened to that vase? I can't believe I thought those glasses were cool. Oh my God.
Now, not all photos will have that new life, but some will, and you can't tell when you take them which ones will. I suspect that, approximately 5% of the photos you take now will have a REALLY important value to you in the future: you just don't know which 5%.
So, the moral here? Store them carefully. DON'T THROW THEM AWAY! Don't delete delete delete. Put them on a hard drive somewhere (hope that you keep a backup: one computer malfunction and it's goodbye Vienna, Venice and anywhere else that you took photos). With any luck, in thirty years they will still be there, and some of them will be REALLY important.