As the others have said it's the ease with which you can send a photo -- it's right there when you open the app. With Messenger you've got a bunch more clicks a

As the others have said it's the ease with which you can send a photo -- it's right there when you open the app. With Messenger you've got a bunch more clicks and a slower camera, and with Insta even more clicks (chat not being a core feature of the app). Thinking about it, there are two major differentiators between Snap and those two. First is the order in which you choose who to send a message to and what the message is. Second is how you can send the same message to multiple people simultaneously. With Messenger & Insta you choose your recipients first, while with Snap you take the picture/video first. This is naturally easier for a spur of the moment message; you don't have to think about who you might want to send it to while the thought is still fresh, or indeed while whatever it is you're snapping is still happening. Snap also has a great model for sending things to multiple people. Say I'm taking a picture my cat doing something silly. It's not interesting enough to go on my story (by whatever metrics I have for that), but I also want to send it to multiple people. There's no way I'm going to create a group just for this; it'll never be used again and there's no reason for the people I choose to be connected with each other. Snap solves this in a way that Messenger and Insta don't (or at least if they do I've not seen it advertised). That's not to say groups aren't really useful -- I'm surprised it took them so long (years?) to implement them.