Aren't you just begging the question here? Personally I don't see why people take pictures of a lot of things. As for preservation -- if you remember it, is it not preserved? And if you somehow forget, could you not forget that you recorded it?
if you don't see the point of people taking pictures and videos of a lot of things in general, then why post it in a thread discussing a device in a product category made specifically for that? It's like saying that you don't see a point of music in a thread with people discussing a new Yamaha piano, and then you attribute that as a disadvantage of that piano.