Sexting on Snapchat is rampant in high school today (I'm a current high school student). The self-destruction principle has allowed for people to feel comfortable about sending explicit photos to eachother -- in relationships, it's almost ubiquitous.

That isn't saying that Snapchat has removed the potential of spreading explicit content. As someone mentioned in another comment, screenshotting the snap circumvents the system. It's also just as easy to take a photo of the screen with another device -- both an untraceable and permanent record of the photo.

As a whole, Snapchat has had a net positive effect for people my age. I can attest that teenagers make unwise decisions now and again, and Snapchat has helped in that those rash decisions are less likely to bite us in the future. While I don't have the data to back up the claim that hundreds of thousands of kids have been protected due to Snapchat's impermanence, I certainly wouldn't be surprised if it was true. It's the most popular social network in my demographic for a reason -- it oozes the ephemeral teenage spirit.