Also things like full text search are super slow over ssh-fs since the network call is intense. Syncing the file system makes things super fast.
They've done a nice job of implementing seamless ssh and tunneling, and it is free to start with. Aside from that, not much.
well there's a file-system sync too, so you can edit code locally and it gets synced in real time with your cloud-based box. This enables you to use SublimeText, Textmate, MacVim or any OS X text editor but with your entire dev environment being hosted on the cloud.