Tiled background question

I found some code online and it works fine. There's a bit of code that can be taken out and it still works. I just wanted to know why it's there.

Both examples below

//stage align/scale stuff
stage.scaleMode = StageScaleMode.NO_SCALE;
stage.align = StageAlign.TOP_LEFT;

//listen to see if the stage is resized
stage.addEventListener(Event.RESIZE, tileBG);

//create a sprite(movieclip without a timeline) called tile
var tile:Sprite;

//function to populate tiled bg onload and onResize
function tileBG(event:Event=null):void {

//create a reference to the old tile container
var oldTile:Sprite = tile;

//create a new tile container
tile = new Sprite();

//fill the container
tile.graphics.beginBitmapFill(new pattern(0, 0));
tile.graphics.drawRect(0, 0, stage.stageWidth, stage.stageHeight);
tile.graphics.endFill();

//add the tile container to the display list
addChild(tile);

//get rid of the old container
if (oldTile != null && oldTile != tile) {
removeChild(oldTile);
}
}
tileBG();

Anyone share some light.

Thanks

Without that code you are just drawing new tiles over the top of the old ones...you can't "see" them but they are still sitting underneath everything taking up memory...the red code makes sure you only keep one 'tile' around at a time.

Thanks for clearing that up.