What is "Real-Time Updates" and Why uses it?

This is how Facebook describes about "Real-Time Updates":

Real-time updates provide you the ability to receive updates about all of your application's users, as their data changes. With such subscriptions, you can be confident that your cached data is correct without polling Facebook's servers, increasing the reliability of your application, and the responsiveness of your user experience.
http://developers.facebook.com/docs/api#realtime

For example,

By implementing real-time updates in our application, the above querying can be removed.

Facebook has already explained well how the real-time updates feature works and the technical details at http://developers.facebook.com/docs/api/realtime. I will be discussing this topic from an implementation point of view, giving you sample code and sharing my experience (as these are probably what you need).

 

How does the Real-Time Updates Work?

The whole work flow of the real-time updates can be explained as follows:

 

In the next part of the tutorial, we will discuss how to implement this feature.