Knowing that what you say will be private(ish) and not be kept on historical record (at least not in public -- I assume Snapchat saves everything) can lead one

Knowing that what you say will be private(ish) and not be kept on historical record (at least not in public -- I assume Snapchat saves everything) can lead one to be more open, honest, and up-front in their communication. Whereas writing something which will be kept on the public historical record for all to see forever leads to both conscious and subconscious self-censorship and can be misleading when trying to "read back who you have been 10 years ago" because what you wrote may not have been what you were really thinking. The ephemeral nature of the spoken word and the historical nature of the written word both have their advantages and disadvantages.