I had my first intern last summer - she's going to college this fall. She used Snapchat throughout the day to communicate with friends. I asked why-- it's non-public, informal, and low-friction in social terms (easier to ask for snap than a phone number). I got the sense that she was continuously lightly dropping in to various group conversations, while simultaneously talking to close friends, often by simply recording reactions on camera.

I've never used Snap so forgive any ignorance on my part.