Difference between returning defer itself and returning defer.promise

Question

What's the difference between returning def and returning def.promise()

var def = $.Deferred();
// some code to set def

return def;
// or
return def.promise();

Answer 1

Deferred can be resolved or rejected by it’s caller. The promise intended to be given to any number of consumers and each will observe the resolution independently.

This concept doesn't allow changing of Deffered's state by consumers, and it's cool feature.

http://blog.mediumequalsmessage.com/promise-deferred-objects-in-javascript-pt1-theory-and-semantics