Snapchat is all about being yourself, and not having to worry about it. Creating such an experience naturally biases the app toward privacy and intimacy, but I wouldn't say the app is for flirting. It just happens to also cater well to those wanting to flirt.
It clicked with me when I watched a video by the CEO [0] where he contrasts the spontaneous, ephemeral expression of identity in Snapchat with the long-lived, accumulated identity in other platforms such as Facebook. Without having to worry about this entire paper trail of your past self, Snapchat sheds a lot of the anxieties that would otherwise inhibit expression.