When using Amazon S3, it's best practice to restrict access to your resources to the people that absolutely need it. The problem is that when companies want to share files they forget to lock down the access again.
With the File Fabric access is always locked and any sharing is done through the security abstraction of the File Fabric. Consider it like a security blanket for your S3 files.
Additionally, new compliance legislation such as GDPR, requires companies to understand 'who' has accessed 'what' and 'when'.
You can enable Cloud Trail of course but the File Fabric provides sophisticated event access logs that make it easy to satisfy legislative procedure such as Subject Access Request's.
Additionally the File Fabric provides enforcement policies to lock down what users can and cannot do to prevent an issues occurring from the onset.
Additionally it is possible to exposes S3 stored data through a secure protocol such as FTPS, SFTP or secure WebDav, and even secure access to it using existing company Identity Access Management solutions such as Active Directory or LDAP.