What happens when you do not use $destroy() after creating an instance using $new() when unit testing AngularJS

I was looking for ways to unit test AngularJs when using the "controller as vm" style. I came across this (Karma jasmine and angular controller using 'Controller as' syntax (this instead of $scope)) question.

The person who provided the answer pointed out that since the "controller as vm" pattern uses this instead of $scope that an instance of $scope must be created.

The person who answered also pointed out that since you are creating an instance that it must be destroyed.

What happens when it is not destroyed?