I'm using amazon s3 as storage for users profile pic. I see that many websites generates large random filenames and put them into the same root directory like:

http://xxx.us-east-1.amazonaws.com/aHR0cHM6Ly9mYmNkbi1wcm9maWxlLWEuYWthbWFpaGQubmV0L2hwcm9maWxlLWFrLWFzaDIvMjczMzkxXzEwMDAwMDMxMjAxMzg5OV81NTk3MjM4Mzdfbi5qcGc.jpg

And my question is: What are the pros and cons of that approach?

If I palce them into different directories, what problems I will have in future?

http://xxx.us-east-1.amazonaws.com/users/id/username.jpg

or

http://xxx.us-east-1.amazonaws.com/users/id/random_number.jpg

Thanks!