Storing data in the cloud allows your application to remember information between launches and to share data among other users, applications, and devices.
Exposing that data via a REST interface makes this data accessible to applications running on a variety of platforms and written in a variety of languages. REST is an architectural pattern for allowing clients to read and update server data through a consistent API. The current implementations of REST uses an HTTP endpoint (a URL) to expose functionality and the features of HTTP (verbs, response codes, and header data) to exchange data between the client and the server.
Azure Mobile Services (ZuMo) makes it easier to expose your data as a REST endpoint by handling the "plumbing" code for you so that you can focus on your data model and your business logic.
With just a few clicks, you can create a service and map it to a database table. ZuMo will create an HTTP endpoint; map HTTP verbs to Create, Read, Update, and Delete methods; create those methods for you; and handle the transformation from JSON data into objects that map to rows in your database table. This isn't impossible code for you to write, but it can be a lot of code. And wouldn't your time be better spent writing the code that makes your application unique?
Azure Mobile Services is a true cross-platform solution that is simple to implement because it handles much of the plumbing code for you.