Aside from the awesome writeup that Hector provided, I just wanted to call this out:

> It works great as a fast way to get your app up and running

It's a really neat and useful tool for prototyping. Obviously as you start to get more and more business logic that should be in your backend, you may want to migrate to your own backend, but if all you need is a simple key:value store, it's great. Heck, it even does files, auth, email, etc. You can take a prototype pretty far before reaching the edge of its usefulness.