[AngularJS] AngularJS 1.3 Performance Improvements - Why are they not enabled by default?

As far as I understand there are two major performance improvements in AngularJS 1.3:

$compileProvider.debugInfoEnabled(false);(https://docs.angularjs.org/guide/production#disabling-debug-data)

and

$httpProvider.useApplyAsync(true);

(https://docs.angularjs.org/api/ng/provider/$httpProvider)

Since these features are not enabled by default, I'm asking myself if there are any reasons not to use them...

Especially $httpProvider.useApplyAsync(true), are there any drawbacks with this?

I'm sure they are not enabled by default so that there's no risk of breaking currently working applications that may rely on some undocumented behaviour, like debug data or any other.