Pro Does not get in the way of what it's designed to do
Snapchat is first and foremost a way to share photos so the first thing that the app presents the user with is the camera enabled and ready to take photos. Once photos or videos are taken, it's possible to caption them or draw on them.
Pro Allows sharing photos, videos and texts that self-destruct
Once a message has been viewed, it gets deleted from Snapchat's servers. Thus, unless a person chooses to save the message manually, there will be no trace of it left. It enables a bit more consequence-free, in-the-moment kind of communication to occur. Additionally you can doodle on photos.
Con Security concerns
In 2013, Snapchat was hacked. As a result phone numbers and usernames of 4.6 million users were published online. That happened after concerns were raised by a security firm weeks before that Snapchat dismissed. Other security concerns were pointed out to Snapchat throughout 2014 including ways that the service could be used for DDOS attacks and how their anti-robot measures can be circumvented.
Snapchat has since implemented two-factor authentication.