Do you need to replace your SFTP server? S3. Do you need to backup TB of db files? S3. Do you need a high performance web cache? S3. Host your SPA? S3 backs cloudfront. Shared filesystem between desktop computers? Probably a bad idea but you can do it with S3. Need a way for customers to securely drop files somewhere? Signed S3 URI. Need to store metrics? Logs? S3. Load balancer logs? S3. And it's cheaper than an EBS volume, and doesn't need resizing every couple of quarters. And there are various SLAs which make it cheaper (Glacier) or more expensive (High Performance). S3 makes a great storage backend for a lot of use cases especially when your data is coming in from multiple regions across the globe. There are some quibbles about eventual consistency but in general it is an easy backend to build for.