I thought that initially (Android, couldn't get it) - I can put filters on my photos in a proper editing package. Then I'd tried it and I was like "oh right, I get it now". I suppose the way it makes sense to me now - my friends put 900 pictures of their holiday on Facebook. They put the one picture that defines their holiday(/day/event) on Instagram. It makes so much difference. Add into that the celebrity voyeurism, and there you have it.