MMS for picture messaging:

* picture quality sucks

* not ephemeral

* requires multiple clicks (snapchat is just one button)

* difficult to BCC (snapchat sending is ALL bcc, which is awesome)

* doesn't work well from country to country (if at all -- but getting snaps from my international friends is really really cool and works the same as local)

* no easy way to send video

* expects a reply

* is awkward to send in the middle of the night (snapchat is 100% non-emergency and just flashes the notification light)

* can't be sure anyone ever got it (snapchat forces read receipts)

*... the list is long.