So far, you’ve built Visualforce pages that have a simple interaction with their controller. They display data from the controller, potentially allowing the user to change it, and then submit it using an action component such as a
commandButton. The action component invokes a method on the controller that returns a
PageReference, navigating the user to a new page or refreshing the current page.
1. It allows actions to run in the background. The user is free to continue working with the page while Force.com processes ...