This Sunday my wife took my phone and just took a silly picture of ourselves during the Super Bowl and sent it to everyone on my list. Within minutes, I was getting a response from pretty much everyone, some people I haven't even talked to in months, and it was fun and made us laugh! I had the dumbest epiphany of my life. It's really just a fast, dumb way to communicate. That's it. Maybe I'll actually use it more now
It reminds me of Facebook back in the day, when it wasn't so serious. When it wasn't full of politics and Buzzfeed and not-so-humblebrags.
You don't have to worry (as much) about a silly photo coming back to haunt you in 10 years on Snapchat. It's much less formal feeling. The faces are my favorite; it's just a lot of fun to use.
We used to have ICQ, AIM, MSN, YIM, and a host of other lesser known methods to chat. This is just one geared toward sending quick pictures. I doubt the privacy part of it is even significant to most users.
Nobody cares what you do in public.
On Snapchat, every picture and chat message self-destructs by default, so there's less social pressure to post something truly extraordinary. There's no publicly visible tracking of likes, so you're not tempted to compare your popularity with others. There is no infinite history where you can come across something old that will make you embarrassed and upset (e.g. records of bad decisions, photos with an ex).
Sending snaps back and forth is great for staying in touch with friends without having to converse about a particular topic. For acquaintances who you don't know as well, an amusing snap is a great icebreaker. And for when you DO want to have a conversation, there's both an IM and a video chat.
The Discover feature where you see content from VIPs directly competes with a significant use-case of Twitter in the target demographic. But unlike Twitter, it's more visual, more immersive, and because of its temporal nature, more exclusive.
Moreover, teens hate creeps. You know every time someone views your snap. You know when someone screenshots your snap. You know when your chat is read. You know when someone views your story. Your audience is exactly who you choose. It's not the internet at large. It's not your mom, it's not the weird guy in your school who found your profile, and it's not people way outside your age-range who are thirst-liking your selfies and making you uncomfortable.
The new 2d printed avatars that allow you to easily add people you meet are perfect. Shows Snapchat really understand their audience.
Snapchat may have been bootstrapped with sexting but it is so much more than that now. They've hit on something that no other social network has - an audience of regular people who aren't selling anything, who want to retain their privacy and who want to have fun with friends and acquiantances online.
So much of the content I see on Snapchat would never be shared anywhere else - and a lot of the people sharing it are those who weren't interested in building a profile on public pages.