On Apple operating systems there is a long tradition of applications crafting beautiful, evocative, sometimes even delicious icons that clearly communicates the spirit of the app. Growing up with this tradition, I have made a habit of creating a distinct visual identity for each project. I treat it as a contract between myself and people that use the app and myself: the icon conveys the fundamental qualities of the experience, things that will remain true forever. I believe that Visual identities express what is unchanging.

Related quote from Seth Godin:

[A brand is not your logo: it's a shorthand for the customer's expectations when they buy from or meet with you. Your brand is the promise they think they're making.]