The service is way more than just a simple front for ssh. The fact that you can boot up a free instance, from anywhere, with access to various ports, means that you could theoretically:
Share files with a friend
Run a (sinatra web app? whatever) and get feedback on it for 20 or so minutes
Do anything that requires a few open ports.
And basically anything else you can think of. (of which, I'm sure I've only scratched the surface)
It's more than just a shared terminal.