I would assume that snapchat doesn't delete your snaps after x amount of hours either. Probably for the same reasons.
> Snapchat servers are designed to automatically delete Snaps after they’ve been viewed by all recipients. Opened Snaps typically cannot be retrieved from Snapchat's servers by anyone, for any reason. Also, Snapchat servers are designed to automatically delete unopened Snaps after 30 days. However, unopened Snaps sent to a Group Chat are deleted by default after 24 hours. [1]
[1] https://support.snapchat.com/en-US/a/when-are-snaps-chats-de...
"You grant Snapchat a world-wide, perpetual, royalty-free, sublicensable, and transferable license to host, store, use, display, reproduce, modify, adapt, edit, publish, create derivative works from, publicly perform, broadcast, distribute, syndicate, promote, exhibit, and publicly display that content in any form and in any and all media or distribution methods,”
In 2014, they were seeing 400 million images per day, 88% of which were to one person [1]. Assuming 0.33 mb/image, no videos, and 100% going to 1 person, that's 132 TB/day.
Per their recent SEC filing, they're now up to 2.5 billion snaps per day. [2]
There's a strong business case for deleting the files as soon as you can. Before they were a gigantic company, their brand trust and keeping things lean encouraged deleting the photos. I believe that holds true today.
[1] http://www.businessinsider.com/how-many-snaps-snapchat-users...
[2] https://www.sec.gov/Archives/edgar/data/1564408/000119312517...
Edit: I decided to run some quick 'n dirty estimation and was a bit surprised by how "cheap" it would actually be to store it all. Snap uses Google Cloud Services, and given their volume, will have a pretty sweet pricing deal. For that reason, I estimated with $0.007/GB, which is the coldline rate per [3] even though they probably wouldn't be doing coldline storage.
Very rough estimate for 1 year of storing every image snap from now until next year is ~13.5 million. At 2.5 billion snaps/day, images only, it would cost ~$5775/month to store all the data generated today.
As an aside, I do wonder if there would be an opportunity for Snap to get and store context from an image without storing the image. It may be a balance between big data and minimizing costs. I'm thinking something along the lines of the list of words from Clarifai [4] stored with the metadata. It wouldn't be very useful to the police because the image recognition is wrong sometimes. "Marijuana" as a tag would be very weak evidence to put forth in court if the police didn't also have the image.
[3] https://cloud.google.com/storage/pricing#storage-pricing
[4] https://developer.clarifai.com/models/aaa03c23b3724a16a56b62...
https://storage.googleapis.com/snap-inc/privacy/lawenforceme...