A brand starts from the first touchpoint of consumer engagement, and many times, that's your app's icon design.
We may all not be app developers, but for those who are, Gizmodo has done a pretty good intro to the pros and cons of different app design for iOS. They’ve recommended the “branded approach”, which allows for great scalability of your app and its brand. However, even though they didn’t classify Instagram’s icon as being a branded, scalable option, I beg to differ that this icon may have become Instagram’s most identifiable aspect’s of it’s visual brand. And today, if we think of the greatest app icons, Instagram is one of the first ones that comes to mind, because of how well it reflects the user experience of the app, combined with the theme of their retro filters. Did I mention that Instagram’s logo is completely different from their app icon? It is, and if you asked me what their logo is, I wouldn’t be able to describe it. Why they decided to design a different logo when their app icon was already a powerful image, makes no sense.