When using $animateCss if the options passed are stored in a variable after the animation the original options object is altered and using it in a new animation will fail (as you can see on codepen http://codepen.io/anon/pen/avWgaX).

If a copy of the configuration object (made using angular.copy) is provided the configuration object is reusable.
But forcing the developer to copy the configuration object each time he wants to use it is quite annoying. And copying the whole object might be a performance bottleneck.

If altering some elements of the configuration object is needed, this should not affect the original provided object.

Tested on Angular 1.4.7