Text message pictures are IME incredibly unreliable and you may be charged for them. And god help you if you accidentally send one internationally; who knows what it might cost?
What? I mean, if YOU are overseas and send a Snapchat, sure. But it's no different from any other data. Sending a MMS picture or video to someone else who is overseas, could be expensive. Snapchat won't incur any fees that all other data wouldn't, such as uploading the picture to Facebook.