This is a filesystem. You mount it directly inside your EC2 boxes and work with it as if it's local (or really NFS-mounted). It's going to be a couple of orders of magnitude faster, but not directly web-connected, so you can't use it to serve content directly as if it was a CDN.

I can see this being useful for a few cases. For one, I can immediately use it for one of the projects I have where I have multiple worker servers and one of them needs to periodically process a few GB's of data, yet I don't want to give that much storage to every sever, and I don't want to make any one server special.

Another use case: you don't know how big your data will grow, yet you want to access it in a random fashion. S3 isn't great for this, but NFS is, and unlimited mounted storage is nice.

Edit: Third use case is logs. You can collect all the logs from all of your servers in one place and access them from any server.