Why do we use @AuraEnabled annotation in Salesforce?

The AuraEnabled annotation provides support for Apex methods and properties to be used with the Lightning Component framework.
The AuraEnabled annotation is overloaded, and is used for two separate and distinct purposes.
1. Use @AuraEnabled on Apex class static methods to make them accessible as remote controller actions in your Lightning components.
2. Use @AuraEnabled on Apex instance methods and properties to make them serializable when an instance of the class is returned as data from a server-side action