We won’t put advertisements in your personal communication – things like Snaps or Chats. That would be totally rude. . . . Understandably, a lot of folks want to know why we’re introducing advertisements to our service. The answer is probably unsurprising – we need to make money.
Users get to choose if they want to watch it by looking at it in Recent Updates or the notification will disappear in 24 hours. The disappearing is key to Snapchat, which was new in the photo-sharing field by allowing messages and photos to last only seconds before disappearing (of course, they aren't really gone for good, as all those leaked Snapchat photos tell you.)
Still, Snapchat needs to make money. Once a super-hot startup, its business model needs to show the business can be solvent or risk becoming absorbed by a bigger tech company. Surely its founders turned down Facebook's $3 billion offer because they had a plan to do this, right?