When I quickly need to cast an object to access a few methods/properties I don’t always want to
create a new casted variable:

var child:DisplayObject = getChildThatMightBeMovieClip();

if (child is MovieClip) {
	var childAsMc:MovieClip = child as MovieClip;
	trace(childAsMc.numChildren);
	trace(childAsMc.currentFrame);
}

or cast it every single time:

var child:DisplayObject = getChildThatMightBeMovieClip();

if (child is MovieClip) {
	trace((child as MovieClip).numChildren);
	trace((child as MovieClip).currentFrame);
}

Using the “with” keyword, we can temporarily cast it without creating a temporary casted variable or casting it again and again:

var child:DisplayObject = getChildThatMightBeMovieClip();

if (child is MovieClip) {
	with (child as MovieClip) {
		trace(numChildren);
		trace(currentFrame);
	}
}

Elegant =)