[detst]

You would want it for the same reason you would want it for any other language.

"upload and go" is a convenience feature of Heroku, not it's reason for existence. It does make it easier to deploy Ruby apps but, again, it's not the reason it exists.

[papachito]

What is the reason for it then? Scaling? But you still have to work on those nasty sql queries. Too bad it doesn't support any nosql database.