This is huge because it means you can use things like S3 Fuse to mount your storage. Which means you can use it to extend your local disk, or run your own backups, or whatever.

Amusingly the price to store 1.2TB of data is the same as the cost of their backup plan, so if your disk is smaller than that, you could save a few bucks running your own backups. Until you have to restore (from what I can tell restores are free on their backup plans but would cost money on the S3 plan).