Flex :: Spark Effects: Why Is Procedural Code Preferred Over Triggers?

In Flex 3, MX effects could be triggered like this:

<mx:Resize id="myEffect" />
<mx:Button mouseDownEffect="{myEffect}" />

In Flex 4, Spark effects are triggered like this:

protected function onClick(event:MouseEvent):void {
resizeEffect.end();
resizeEffect.play();[code]....

There might be small differences between mouseDown trigger and the click event, please ignore that, it's just an example.I'm not sure whether triggers would or would not work reliably for Spark effects. Maybe they would but I guess there is a reason why this possibility is not even mentioned in the official docs.